diff --git a/src/actions/profile-view.ts b/src/actions/profile-view.ts
index 9ca988d8cc..2e8cb89717 100644
--- a/src/actions/profile-view.ts
+++ b/src/actions/profile-view.ts
@@ -1271,9 +1271,10 @@ function _findOtherVisibleThread(
     const localTracks = getLocalTracks(getState(), globalTrack.pid);
     const localTrackOrder = getLocalTrackOrder(getState(), globalTrack.pid);
     const hiddenLocalTracks = getHiddenLocalTracks(getState(), globalTrack.pid);
-    const localTrackIndexesToIgnore = localTrackIndexesToIgnoreByPid
-      ? (localTrackIndexesToIgnoreByPid.get(globalTrack.pid) ?? new Set())
-      : new Set();
+    const localTrackIndexesToIgnore: Set<TrackIndex> =
+      localTrackIndexesToIgnoreByPid
+        ? (localTrackIndexesToIgnoreByPid.get(globalTrack.pid) ?? new Set())
+        : new Set();
 
     for (const trackIndex of localTrackOrder) {
       const track = localTracks[trackIndex];
diff --git a/src/app-logic/url-handling.ts b/src/app-logic/url-handling.ts
index 60267bbc77..c3e1e9e3fa 100644
--- a/src/app-logic/url-handling.ts
+++ b/src/app-logic/url-handling.ts
@@ -635,7 +635,7 @@ function convertHiddenLocalTracksByPidFromString(
     return new Map();
   }
 
-  const hiddenLocalTracksByPid = new Map();
+  const hiddenLocalTracksByPid: Map<Pid, Set<TrackIndex>> = new Map();
 
   for (const stringPart of rawText.split('~')) {
     if (!stringPart.includes('-')) {
@@ -679,7 +679,7 @@ function convertLocalTrackOrderByPidFromString(
     return new Map();
   }
 
-  const localTrackOrderByPid = new Map();
+  const localTrackOrderByPid: Map<Pid, TrackIndex[]> = new Map();
 
   for (const stringPart of rawText.split('~')) {
     if (!stringPart.includes('-')) {
@@ -1018,12 +1018,10 @@ const _upgraders: {
         .join('~');
     }
     if (query.thread) {
-      const selectedThreads = new Set(
+      const selectedThreads: Set<number> = new Set(
         query.thread.split(',').map((n: string) => +n)
       );
-      query.thread = encodeUintSetForUrlComponent(
-        selectedThreads as Set<number>
-      );
+      query.thread = encodeUintSetForUrlComponent(selectedThreads);
     }
 
     // In this version, uintarray-encoding started supporting a range syntax:
diff --git a/src/components/shared/AssemblyView-codemirror.tsx b/src/components/shared/AssemblyView-codemirror.tsx
index d1eba6e92e..12385ae8b9 100644
--- a/src/components/shared/AssemblyView-codemirror.tsx
+++ b/src/components/shared/AssemblyView-codemirror.tsx
@@ -149,7 +149,7 @@ function addressTimingsToLineTimings(
   addressTimings: AddressTimings,
   map: AddressToLineMap
 ): LineTimings {
-  const totalLineHits = new Map();
+  const totalLineHits: Map<LineNumber, number> = new Map();
   for (const [address, hitCount] of addressTimings.totalAddressHits) {
     const line = map.addressToLine(address);
     if (line !== null) {
@@ -158,7 +158,7 @@ function addressTimingsToLineTimings(
     }
   }
 
-  const selfLineHits = new Map();
+  const selfLineHits: Map<LineNumber, number> = new Map();
   for (const [address, hitCount] of addressTimings.selfAddressHits) {
     const line = map.addressToLine(address);
     if (line !== null) {
diff --git a/src/components/tooltip/GCMarker.tsx b/src/components/tooltip/GCMarker.tsx
index b9dd40603b..72576194f3 100644
--- a/src/components/tooltip/GCMarker.tsx
+++ b/src/components/tooltip/GCMarker.tsx
@@ -466,7 +466,7 @@ function _filterInterestingPhaseTimes(
   /*
    * Build the tree.
    */
-  const tree = new Map();
+  const tree: Map<string, PhaseTreeNode> = new Map();
   for (const phase of phaseTimes) {
     const components = phase.name.split('.');
     _treeInsert(tree, components, phase);
diff --git a/src/profile-logic/call-node-info.ts b/src/profile-logic/call-node-info.ts
index 6c0a90e7db..c6406916f4 100644
--- a/src/profile-logic/call-node-info.ts
+++ b/src/profile-logic/call-node-info.ts
@@ -1161,7 +1161,7 @@ export class CallNodeInfoInverted implements CallNodeInfo {
     // Pass 1: Count the deep nodes per func, and build up a list of funcs.
     // We will need to create a child for each deep node func, and each child will
     // need to know how many deep nodes it has.
-    const deepNodeCountPerFunc = new Map();
+    const deepNodeCountPerFunc: Map<IndexIntoFuncTable, number> = new Map();
     const callNodeTable = this._callNodeTable;
     for (let i = 0; i < parentDeepNodeCount; i++) {
       const selfNode = parentSelfNodes[i];
@@ -1212,7 +1212,7 @@ export class CallNodeInfoInverted implements CallNodeInfo {
     // partitions; one partition per child, in the right order.
     const startIndexPerChild = new Uint32Array(childCount);
     const deepNodeCountPerChild = new Uint32Array(childCount);
-    const funcToChildIndex = new Map();
+    const funcToChildIndex: Map<IndexIntoFuncTable, number> = new Map();
 
     let nextChildStartIndex = 0;
     for (let childIndex = 0; childIndex < childCount; childIndex++) {
diff --git a/src/profile-logic/import/art-trace.ts b/src/profile-logic/import/art-trace.ts
index 4e3d805c6d..b2d47f0679 100644
--- a/src/profile-logic/import/art-trace.ts
+++ b/src/profile-logic/import/art-trace.ts
@@ -3,6 +3,11 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 // Parses the ART trace format and converts it to the Gecko profile format.
 
+import type {
+  IndexIntoFrameTable,
+  IndexIntoStackTable,
+} from 'firefox-profiler/types';
+
 // These profiles are obtained from Android in two ways:
 //  - Programmatically, from the Debug API: https://developer.android.com/studio/profile/cpu-profiler#debug-api
 //  - Or via the profiler UI in Android Studio.
@@ -562,7 +567,7 @@ function procureSamplingInterval(trace: ArtTrace) {
 
   // Gather up to 500 time deltas between method actions on a thread.
   const deltas: number[] = [];
-  const previousTimestampByThread = new Map();
+  const previousTimestampByThread: Map<number, number> = new Map();
   const numberOfActionsToConsider = Math.min(500, methodActions.length);
   for (let i = 0; i < numberOfActionsToConsider; i++) {
     const { tid, globalTime } = methodActions[i];
@@ -617,7 +622,7 @@ export function getSpecialCategory(
     return s.substring(0, firstPeriodPos);
   }
 
-  const significantSegmentCounter = new Map();
+  const significantSegmentCounter: Map<string, number> = new Map();
   for (let i = 0; i < methods.length; i++) {
     const significantSegment = getSignificantNamespaceSegment(
       methods[i].className
@@ -787,8 +792,8 @@ class ThreadBuilder {
 
   _currentStack: number | null = null;
   _nextSampleTimestamp = 0;
-  _stackMap = new Map();
-  _frameMap = new Map();
+  _stackMap: Map<string, IndexIntoStackTable> = new Map();
+  _frameMap: Map<number, IndexIntoFrameTable> = new Map();
   _registerTime = 0;
   _name;
   _pid;
@@ -939,7 +944,7 @@ export function convertArtTraceProfile(
   const { summaryDetails, threads, methods, methodActions } = trace;
   const categoryInfo = new CategoryInfo(methods);
   const methodMap = new Map(methods.map((m) => [m.methodId, m]));
-  const threadBuilderMap = new Map();
+  const threadBuilderMap: Map<number, ThreadBuilder> = new Map();
 
   if (methodActions.length > 0) {
     for (let i = 0; i < methodActions.length; i++) {
diff --git a/src/profile-logic/import/chrome.ts b/src/profile-logic/import/chrome.ts
index 63d2f6c2c6..6aa61ae8ce 100644
--- a/src/profile-logic/import/chrome.ts
+++ b/src/profile-logic/import/chrome.ts
@@ -396,10 +396,11 @@ function getThreadInfo(
 
   profile.threads.push(thread);
 
-  const nodeIdToStackId = new Map();
+  const nodeIdToStackId: Map<number | void, IndexIntoStackTable | null> =
+    new Map();
   nodeIdToStackId.set(undefined, null);
 
-  const threadInfo = {
+  const threadInfo: ThreadInfo = {
     thread,
     nodeIdToStackId,
     funcKeyToFuncId: new Map(),
@@ -518,8 +519,8 @@ async function processTracingEvents(
     ensureExists(profile.meta.categories)
   );
 
-  const threadInfoByPidAndTid = new Map();
-  const threadInfoByThread = new Map();
+  const threadInfoByPidAndTid: Map<string, ThreadInfo> = new Map();
+  const threadInfoByThread: Map<RawThread, ThreadInfo> = new Map();
   for (const profileEvent of profileEvents) {
     // The thread info is all of the data that makes it possible to process an
     // individual thread.
@@ -574,7 +575,7 @@ async function processTracingEvents(
       } = thread;
 
       if (nodes) {
-        const parentMap = new Map();
+        const parentMap: Map<number, number> = new Map();
         for (const node of nodes) {
           const { callFrame, id: nodeIndex } = node;
           let parent: number | void = undefined;
diff --git a/src/profile-logic/import/linux-perf.ts b/src/profile-logic/import/linux-perf.ts
index b20c6185b5..8daf8f6782 100644
--- a/src/profile-logic/import/linux-perf.ts
+++ b/src/profile-logic/import/linux-perf.ts
@@ -2,7 +2,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-import type { MixedObject } from 'firefox-profiler/types';
+import type {
+  IndexIntoFrameTable,
+  IndexIntoStackTable,
+  MixedObject,
+} from 'firefox-profiler/types';
 
 /**
  * The "perf script" format is the plain text format that is output by an
@@ -118,7 +122,7 @@ export function convertPerfScriptProfile(
     };
     const stringTable: string[] = [];
 
-    const stackMap = new Map();
+    const stackMap: Map<string, IndexIntoStackTable> = new Map();
     function getOrCreateStack(frame: number, prefix: number | null) {
       const key = prefix === null ? `${frame}` : `${frame},${prefix}`;
       let stack = stackMap.get(key);
@@ -130,7 +134,7 @@ export function convertPerfScriptProfile(
       return stack;
     }
 
-    const frameMap = new Map();
+    const frameMap: Map<string, IndexIntoFrameTable> = new Map();
     function getOrCreateFrame(frameString: string): number {
       let frame = frameMap.get(frameString);
       if (frame === undefined) {
diff --git a/src/profile-logic/js-tracer.tsx b/src/profile-logic/js-tracer.tsx
index 2a18d95e13..43fb52c42b 100644
--- a/src/profile-logic/js-tracer.tsx
+++ b/src/profile-logic/js-tracer.tsx
@@ -38,7 +38,7 @@ function getScriptLocationToFuncIndex(
   sources: SourceTable
 ): ScriptLocationToFuncIndex {
   const { funcTable } = thread;
-  const scriptLocationToFuncIndex = new Map();
+  const scriptLocationToFuncIndex: ScriptLocationToFuncIndex = new Map();
   for (let funcIndex = 0; funcIndex < funcTable.length; funcIndex++) {
     if (!funcTable.isJS[funcIndex]) {
       continue;
diff --git a/src/profile-logic/marker-data.ts b/src/profile-logic/marker-data.ts
index f8abcce05c..fba90cc7d6 100644
--- a/src/profile-logic/marker-data.ts
+++ b/src/profile-logic/marker-data.ts
@@ -484,7 +484,7 @@ export function correlateIPCMarkers(
       recvThreadName: formatThreadName(recvTid),
     };
 
-    const addedThreadIds = new Set();
+    const addedThreadIds: Set<number> = new Set();
     if (startEndpointMarker) {
       addedThreadIds.add(startEndpointMarker.tid);
       correlations.set(
@@ -1331,7 +1331,7 @@ export function groupScreenshotsById(
   getMarker: (markerIndex: MarkerIndex) => Marker,
   markerIndexes: MarkerIndex[]
 ): Map<string, Marker[]> {
-  const idToScreenshotMarkers = new Map();
+  const idToScreenshotMarkers: Map<string, Marker[]> = new Map();
   for (const markerIndex of markerIndexes) {
     const marker = getMarker(markerIndex);
     const { data } = marker;
diff --git a/src/profile-logic/marker-schema.tsx b/src/profile-logic/marker-schema.tsx
index ec392732b2..fd56e9ba34 100644
--- a/src/profile-logic/marker-schema.tsx
+++ b/src/profile-logic/marker-schema.tsx
@@ -674,7 +674,7 @@ export function markerPayloadMatchesSearch(
 export function computeStringIndexMarkerFieldsByDataType(
   markerSchemas: MarkerSchema[]
 ): Map<string, string[]> {
-  const stringIndexMarkerFieldsByDataType = new Map();
+  const stringIndexMarkerFieldsByDataType: Map<string, string[]> = new Map();
 
   // 'CompositorScreenshot' markers currently don't have a schema (#5303),
   // hardcode the url field (which is a string index) until they do.
diff --git a/src/profile-logic/merge-compare.ts b/src/profile-logic/merge-compare.ts
index be1bdaabdd..8f3337a9fd 100644
--- a/src/profile-logic/merge-compare.ts
+++ b/src/profile-logic/merge-compare.ts
@@ -444,7 +444,7 @@ function mergeCategories(categoriesPerProfile: Array<CategoryList | void>): {
   const newCategoryIndexByName: Map<string, IndexIntoCategoryList> = new Map();
 
   const translationMaps = categoriesPerProfile.map((categories) => {
-    const translationMap = new Map();
+    const translationMap: TranslationMapForCategories = new Map();
 
     if (!categories) {
       // Profiles that are imported may not have categories. Ignore it when attempting
@@ -482,7 +482,7 @@ function mergeStringArrays(stringArraysPerProfile: Array<string[]>): {
   const newStringTable = StringTable.withBackingArray(newStringArray);
 
   const translationMaps = stringArraysPerProfile.map((stringArray) => {
-    const translationMap = new Map();
+    const translationMap: TranslationMapForStrings = new Map();
     for (let i = 0; i < stringArray.length; i++) {
       translationMap.set(i, newStringTable.indexForString(stringArray[i]));
     }
@@ -503,7 +503,7 @@ function mergeSources(
   const mapOfInsertedSources: Map<string, IndexIntoSourceTable> = new Map();
 
   const translationMaps = sourcesPerProfile.map((sources, profileIndex) => {
-    const translationMap = new Map();
+    const translationMap: TranslationMapForSources = new Map();
     if (!sources) {
       return translationMap;
     }
@@ -725,11 +725,11 @@ function mergeLibs(libsPerProfile: Lib[][]): {
 } {
   const mapOfInsertedLibs: Map<string, IndexIntoLibs> = new Map();
 
-  const translationMaps: Array<Map<IndexIntoLibs, IndexIntoLibs>> = [];
+  const translationMaps: Array<TranslationMapForLibs> = [];
   const newLibTable: Lib[] = [];
 
   for (const libs of libsPerProfile) {
-    const translationMap = new Map();
+    const translationMap: TranslationMapForLibs = new Map();
 
     libs.forEach((lib, i) => {
       const insertedLibKey = [lib.name, lib.debugName].join('#');
@@ -765,7 +765,7 @@ function combineResourceTables(threads: ReadonlyArray<RawThread>): {
   const newResourceTable = getEmptyResourceTable();
 
   threads.forEach((thread) => {
-    const translationMap = new Map();
+    const translationMap: TranslationMapForResources = new Map();
     const { resourceTable } = thread;
 
     for (let i = 0; i < resourceTable.length; i++) {
@@ -811,7 +811,7 @@ function combineNativeSymbolTables(threads: ReadonlyArray<RawThread>): {
   const newNativeSymbols = getEmptyNativeSymbolTable();
 
   threads.forEach((thread) => {
-    const translationMap = new Map();
+    const translationMap: TranslationMapForNativeSymbols = new Map();
     const { nativeSymbols } = thread;
 
     for (let i = 0; i < nativeSymbols.length; i++) {
@@ -861,7 +861,7 @@ function combineFuncTables(
 
   threads.forEach((thread, threadIndex) => {
     const { funcTable } = thread;
-    const translationMap = new Map();
+    const translationMap: TranslationMapForFuncs = new Map();
     const resourceTranslationMap = translationMapsForResources[threadIndex];
 
     for (let i = 0; i < funcTable.length; i++) {
@@ -931,7 +931,7 @@ function combineFrameTables(
 
   threads.forEach((thread, threadIndex) => {
     const { frameTable } = thread;
-    const translationMap = new Map();
+    const translationMap: TranslationMapForFrames = new Map();
     const funcTranslationMap = translationMapsForFuncs[threadIndex];
     const nativeSymbolTranslationMap =
       translationMapsForNativeSymbols[threadIndex];
@@ -993,7 +993,7 @@ function combineStackTables(
 
   threads.forEach((thread, threadIndex) => {
     const { stackTable } = thread;
-    const translationMap = new Map();
+    const translationMap: TranslationMapForStacks = new Map();
     const frameTranslationMap = translationMapsForFrames[threadIndex];
 
     for (let i = 0; i < stackTable.length; i++) {
@@ -1042,7 +1042,7 @@ function combineSamplesDiffing(
     ThreadAndWeightMultiplier,
   ]
 ): { samples: RawSamplesTable; translationMaps: TranslationMapForSamples[] } {
-  const translationMaps = [new Map(), new Map()];
+  const translationMaps: TranslationMapForSamples[] = [new Map(), new Map()];
   const [
     {
       thread: { samples: samples1, tid: tid1 },
@@ -1427,7 +1427,7 @@ function mergeMarkers(
 
   threads.forEach((thread, threadIndex) => {
     const translationMapForStacks = translationMapsForStacks[threadIndex];
-    const translationMap = new Map();
+    const translationMap: TranslationMapForMarkers = new Map();
     const { markers } = thread;
 
     for (let markerIndex = 0; markerIndex < markers.length; markerIndex++) {
diff --git a/src/profile-logic/mozilla-symbolication-api.ts b/src/profile-logic/mozilla-symbolication-api.ts
index 2c8ecfc092..17fff7f637 100644
--- a/src/profile-logic/mozilla-symbolication-api.ts
+++ b/src/profile-logic/mozilla-symbolication-api.ts
@@ -202,7 +202,7 @@ function getV5ResultForLibRequest(
     );
   }
 
-  const results = new Map();
+  const results: Map<number, AddressResult> = new Map();
   for (let i = 0; i < addressInfo.length; i++) {
     const address = addressArray[i];
     const info = addressInfo[i];
diff --git a/src/profile-logic/process-profile.ts b/src/profile-logic/process-profile.ts
index 7a363ec58d..72f5d26a58 100644
--- a/src/profile-logic/process-profile.ts
+++ b/src/profile-logic/process-profile.ts
@@ -99,6 +99,7 @@ import type {
   Pid,
   GeckoMarkerSchema,
   GeckoSourceTable,
+  IndexIntoCategoryList,
 } from 'firefox-profiler/types';
 import { decompress, isGzip } from 'firefox-profiler/utils/gz';
 
@@ -1548,7 +1549,8 @@ export function insertExternalMarkersIntoProfile(
     }
   }
 
-  const categoryMap = new Map();
+  const categoryMap: Map<IndexIntoCategoryList, IndexIntoCategoryList> =
+    new Map();
   for (let i = 0; i < externalMarkers.categories.length; ++i) {
     const cat = externalMarkers.categories[i];
     let index = geckoProfile.meta.categories.findIndex(
diff --git a/src/profile-logic/profile-data.ts b/src/profile-logic/profile-data.ts
index 7c9b4911ae..7b31e1361c 100644
--- a/src/profile-logic/profile-data.ts
+++ b/src/profile-logic/profile-data.ts
@@ -2920,7 +2920,10 @@ export function reserveFunctionsInThread(
   thread: Thread
 ): ThreadWithReservedFunctions {
   const funcTable = shallowCloneFuncTable(thread.funcTable);
-  const reservedFunctionsForResources = new Map();
+  const reservedFunctionsForResources: Map<
+    IndexIntoResourceTable,
+    IndexIntoFuncTable
+  > = new Map();
   const jsResourceTypes = [
     resourceTypes.addon,
     resourceTypes.url,
@@ -3271,7 +3274,7 @@ export function extractProfileFilterPageData(
     return new Map();
   }
 
-  const pageDataByTabID = new Map();
+  const pageDataByTabID: Map<TabID, ProfileFilterPageData> = new Map();
   for (const [tabID, pages] of pagesMapByTabID) {
     let topMostPages = pages.filter(
       (page) =>
@@ -3643,7 +3646,7 @@ export function nudgeReturnAddresses(thread: RawThread): RawThread {
   // These are the top ("self") frames of stacks from sampling.
   // In the variable names below, ip means "instruction pointer".
   const oldIpFrameToNewIpFrame = new Uint32Array(frameTable.length);
-  const ipFrames = new Set();
+  const ipFrames: Set<IndexIntoFrameTable> = new Set();
   for (const stack of samplingSelfStacks) {
     const frame = stackTable.frame[stack];
     oldIpFrameToNewIpFrame[frame] = frame;
@@ -3728,8 +3731,14 @@ export function nudgeReturnAddresses(thread: RawThread): RawThread {
 
   // Make a new stack table which refers to the adjusted frames.
   const newStackTable = getEmptyRawStackTable();
-  const mapForSamplingSelfStacks = new Map();
-  const mapForBacktraceSelfStacks = new Map();
+  const mapForSamplingSelfStacks: Map<
+    null | IndexIntoStackTable,
+    null | IndexIntoStackTable
+  > = new Map();
+  const mapForBacktraceSelfStacks: Map<
+    null | IndexIntoStackTable,
+    null | IndexIntoStackTable
+  > = new Map();
   const prefixMap = new Uint32Array(stackTable.length);
   for (let stack = 0; stack < stackTable.length; stack++) {
     const frame = stackTable.frame[stack];
@@ -4043,7 +4052,7 @@ export function computeTabToThreadIndexesMap(
   threads: RawThread[],
   innerWindowIDToTabMap: Map<InnerWindowID, TabID> | null
 ): Map<TabID, Set<ThreadIndex>> {
-  const tabToThreadIndexesMap = new Map();
+  const tabToThreadIndexesMap: Map<TabID, Set<ThreadIndex>> = new Map();
   if (!innerWindowIDToTabMap) {
     // There is no pages information in the profile, return an empty map.
     return tabToThreadIndexesMap;
diff --git a/src/profile-logic/symbol-store.ts b/src/profile-logic/symbol-store.ts
index abc5950c4c..622f44b644 100644
--- a/src/profile-logic/symbol-store.ts
+++ b/src/profile-logic/symbol-store.ts
@@ -106,7 +106,7 @@ export function readSymbolsFromSymbolTable(
   // the symbolTableIndex array.
   // Both addressArray and symbolTableAddrs are sorted in ascending order.
   const decoder = new TextDecoder();
-  const results = new Map();
+  const results: Map<number, AddressResult> = new Map();
   let currentSymbolIndex = undefined;
   let currentSymbol = '';
   let currentSymbolFunctionSize = undefined;
diff --git a/src/profile-logic/symbolication.ts b/src/profile-logic/symbolication.ts
index e812602ec7..5b19e499f6 100644
--- a/src/profile-logic/symbolication.ts
+++ b/src/profile-logic/symbolication.ts
@@ -240,8 +240,8 @@ type ThreadSymbolicationInfo = Map<LibKey, ThreadLibSymbolicationInfo>;
 function makeConsensusMap<K, V>(
   iterableOfEntryPairs: Iterable<[K, V]>
 ): Map<K, V> {
-  const consensusMap = new Map();
-  const divergentKeys = new Set();
+  const consensusMap: Map<K, V> = new Map();
+  const divergentKeys: Set<K> = new Set();
   for (const [key, value] of iterableOfEntryPairs) {
     if (divergentKeys.has(key)) {
       continue;
@@ -270,7 +270,7 @@ function getThreadSymbolicationInfo(
 ): ThreadSymbolicationInfo {
   const { frameTable, funcTable, nativeSymbols, resourceTable } = thread;
 
-  const map = new Map();
+  const map: ThreadSymbolicationInfo = new Map();
   for (
     let resourceIndex = 0;
     resourceIndex < resourceTable.length;
@@ -292,7 +292,7 @@ function getThreadSymbolicationInfo(
     }
 
     // Collect the set of funcs for this library in this thread.
-    const allFuncsForThisLib = new Set();
+    const allFuncsForThisLib: Set<IndexIntoFuncTable> = new Set();
     for (let funcIndex = 0; funcIndex < funcTable.length; funcIndex++) {
       if (funcTable.resource[funcIndex] !== resourceIndex) {
         continue;
@@ -301,7 +301,8 @@ function getThreadSymbolicationInfo(
     }
 
     // Collect the set of native symbols for this library in this thread.
-    const allNativeSymbolsForThisLib = new Set();
+    const allNativeSymbolsForThisLib: Set<IndexIntoNativeSymbolTable> =
+      new Set();
     for (
       let nativeSymbolIndex = 0;
       nativeSymbolIndex < nativeSymbols.length;
@@ -343,7 +344,7 @@ function getThreadSymbolicationInfo(
 function buildLibSymbolicationRequestsForAllThreads(
   symbolicationInfo: ThreadSymbolicationInfo[]
 ): LibSymbolicationRequest[] {
-  const libKeyToAddressesMap = new Map();
+  const libKeyToAddressesMap: Map<string, Set<number>> = new Map();
   for (const threadSymbolicationInfo of symbolicationInfo) {
     for (const [libKey, { frameAddresses }] of threadSymbolicationInfo) {
       let addressSet = libKeyToAddressesMap.get(libKey);
@@ -478,10 +479,13 @@ export function applySymbolicationSteps(
   shared: RawProfileSharedData,
   symbolicationSteps: SymbolicationStepInfo[]
 ): { thread: RawThread; oldFuncToNewFuncsMap: FuncToFuncsMap } {
-  const oldFuncToNewFuncsMap = new Map();
+  const oldFuncToNewFuncsMap: FuncToFuncsMap = new Map();
   const frameCount = oldThread.frameTable.length;
   const shouldStacksWithThisFrameBeRemoved = new Uint8Array(frameCount);
-  const frameIndexToInlineExpansionFrames = new Map();
+  const frameIndexToInlineExpansionFrames: Map<
+    IndexIntoFrameTable,
+    IndexIntoFrameTable[]
+  > = new Map();
   let thread = oldThread;
   for (const symbolicationStep of symbolicationSteps) {
     thread = _partiallyApplySymbolicationStep(
@@ -716,7 +720,7 @@ function _partiallyApplySymbolicationStep(
   const availableFuncIter = availableFuncs.values();
 
   // funcKey -> funcIndex, where funcKey = `${nameStringIndex}:${fileStringIndex}`
-  const funcKeyToFuncMap = new Map();
+  const funcKeyToFuncMap: Map<string, IndexIntoFuncTable> = new Map();
 
   const availableFrameIter = inlinedFrames.values();
   const oldFuncToNewFuncsEntries: Array<[IndexIntoFuncTable, string]> = [];
diff --git a/src/profile-logic/tracks.ts b/src/profile-logic/tracks.ts
index 44277e17b5..8a6852f12e 100644
--- a/src/profile-logic/tracks.ts
+++ b/src/profile-logic/tracks.ts
@@ -239,7 +239,7 @@ export function initializeLocalTrackOrderByPid(
   legacyThreadOrder: ThreadIndex[] | null,
   profile: Profile | null
 ): Map<Pid, TrackIndex[]> {
-  const trackOrderByPid = new Map();
+  const trackOrderByPid: Map<Pid, TrackIndex[]> = new Map();
 
   if (legacyThreadOrder === null) {
     // Go through each set of tracks, determine the sort order.
@@ -310,7 +310,7 @@ export function computeLocalTracksByPid(
   profile: Profile,
   availableGlobalTracks: GlobalTrack[]
 ): Map<Pid, LocalTrack[]> {
-  const localTracksByPid = new Map();
+  const localTracksByPid: Map<Pid, LocalTrack[]> = new Map();
 
   // Create a new set of available pids, so we can filter out the local tracks
   // if their globalTracks are also filtered out by the tab selector.
@@ -448,7 +448,7 @@ export function addEventDelayTracksForThreads(
   threads: RawThread[],
   localTracksByPid: Map<Pid, LocalTrack[]>
 ): Map<Pid, LocalTrack[]> {
-  const newLocalTracksByPid = new Map();
+  const newLocalTracksByPid: Map<Pid, LocalTrack[]> = new Map();
 
   for (let threadIndex = 0; threadIndex < threads.length; threadIndex++) {
     const thread = threads[threadIndex];
@@ -909,7 +909,7 @@ export function tryInitializeHiddenTracksFromUrl(
     urlHiddenGlobalTracks
   );
 
-  const hiddenLocalTracksByPid = new Map();
+  const hiddenLocalTracksByPid: Map<Pid, Set<TrackIndex>> = new Map();
   for (const [pid, localTrackOrder] of tracksWithOrder.localTrackOrderByPid) {
     const localTracks = new Set(localTrackOrder);
     const hiddenLocalTracks = intersectSets(
@@ -987,7 +987,7 @@ function _computeHiddenTracksForVisibleThreads(
     })
   );
 
-  const hiddenLocalTracksByPid = new Map();
+  const hiddenLocalTracksByPid: Map<Pid, Set<ThreadIndex>> = new Map();
   for (const [pid, localTrackOrder] of tracksWithOrder.localTrackOrderByPid) {
     if (!visiblePids.has(pid)) {
       // Hide all local tracks.
@@ -1520,7 +1520,7 @@ export function getSearchFilteredLocalTracksByPid(
     return null;
   }
 
-  const searchFilteredLocalTracksByPid = new Map();
+  const searchFilteredLocalTracksByPid: Map<Pid, Set<TrackIndex>> = new Map();
   for (const [pid, tracks] of localTracksByPid) {
     const searchFilteredLocalTracks = new Set<TrackIndex>();
     const localTrackNames = localTrackNamesByPid.get(pid);
@@ -1640,7 +1640,7 @@ export function getTypeFilteredLocalTracksByPid(
     return null;
   }
 
-  const typeFilteredLocalTracksByPid = new Map();
+  const typeFilteredLocalTracksByPid: Map<Pid, Set<TrackIndex>> = new Map();
   for (const [pid, tracks] of localTracksByPid) {
     const typeFilteredLocalTracks = new Set<TrackIndex>();
 
diff --git a/src/profile-logic/transforms.ts b/src/profile-logic/transforms.ts
index a1f373579f..c5c1910d04 100644
--- a/src/profile-logic/transforms.ts
+++ b/src/profile-logic/transforms.ts
@@ -1383,7 +1383,10 @@ export function focusInvertedSubtree(
       return null;
     }
 
-    const oldStackToNewStack = new Map();
+    const oldStackToNewStack: Map<
+      IndexIntoStackTable | null,
+      IndexIntoStackTable | null
+    > = new Map();
     // A root stack's prefix will be null. Maintain that relationship from old to new
     // stacks by mapping from null to null.
     oldStackToNewStack.set(null, null);
diff --git a/src/selectors/app.tsx b/src/selectors/app.tsx
index 65cb1d043e..aeeb8de6ea 100644
--- a/src/selectors/app.tsx
+++ b/src/selectors/app.tsx
@@ -35,6 +35,7 @@ import type {
   ThreadsKey,
   ExperimentalFlags,
   UploadedProfileInformation,
+  Pid,
 } from 'firefox-profiler/types';
 import type { TabSlug } from 'firefox-profiler/app-logic/tabs-handling';
 import type {
@@ -148,7 +149,7 @@ export const getTimelineHeight: Selector<null | CssPixels> = createSelector(
     }
 
     // Figure out which PIDs are hidden.
-    const hiddenPids = new Set();
+    const hiddenPids: Set<Pid> = new Set();
     for (const trackIndex of hiddenGlobalTracks) {
       const globalTrack = globalTracks[trackIndex];
       if (globalTrack.type === 'process') {
diff --git a/src/selectors/profile.ts b/src/selectors/profile.ts
index 38d2e68e9e..45852c231a 100644
--- a/src/selectors/profile.ts
+++ b/src/selectors/profile.ts
@@ -575,7 +575,7 @@ export const getLocalTrackNamesByPid: Selector<Map<Pid, string[]>> =
     getRawProfileSharedData,
     getCounters,
     (localTracksByPid, threads, shared, counters) => {
-      const localTrackNamesByPid = new Map();
+      const localTrackNamesByPid: Map<Pid, string[]> = new Map();
       for (const [pid, localTracks] of localTracksByPid) {
         localTrackNamesByPid.set(
           pid,
@@ -749,7 +749,7 @@ export const getInnerWindowIDSetByTabID: Selector<Map<
     return null;
   }
 
-  const innerWindowIDSetByTabID = new Map();
+  const innerWindowIDSetByTabID: Map<TabID, Set<InnerWindowID>> = new Map();
   for (const [tabID, pages] of pagesMap) {
     innerWindowIDSetByTabID.set(
       tabID,
@@ -765,7 +765,7 @@ export const getExtensionIdToNameMap: Selector<Map<string, string> | null> =
       return null;
     }
 
-    const extensionIDtoNameMap = new Map();
+    const extensionIDtoNameMap: Map<string, string> = new Map();
     for (let i = 0; i < extensions.length; i++) {
       extensionIDtoNameMap.set(extensions.baseURL[i], extensions.name[i]);
     }
@@ -834,7 +834,7 @@ export const getProfileFilterSortedPageData: Selector<SortedTabPageData> =
 export const getThreadIdToNameMap: Selector<Map<Tid, string>> = createSelector(
   getThreads,
   (threads) => {
-    const threadIdToNameMap = new Map();
+    const threadIdToNameMap: Map<Tid, string> = new Map();
     for (const thread of threads) {
       threadIdToNameMap.set(thread.tid, getFriendlyThreadName(threads, thread));
     }
@@ -845,7 +845,7 @@ export const getThreadIdToNameMap: Selector<Map<Tid, string>> = createSelector(
 export const getProcessIdToNameMap: Selector<Map<Pid, string>> = createSelector(
   getThreads,
   (threads) => {
-    const processIdToNameMap = new Map();
+    const processIdToNameMap: Map<Pid, string> = new Map();
     for (const thread of threads) {
       if (!thread.isMainThread || !thread.pid) {
         continue;