diff --git a/browser/base/content/test/performance/browser_startup_content.js b/browser/base/content/test/performance/browser_startup_content.js
index e5b357f54686..741d3111ab7d 100644
--- a/browser/base/content/test/performance/browser_startup_content.js
+++ b/browser/base/content/test/performance/browser_startup_content.js
@@ -60,7 +60,7 @@ const known_scripts = {
 
 if (!gFissionBrowser) {
   known_scripts.modules.add(
-    "resource:///modules/sessionstore/ContentSessionStore.jsm"
+    "resource:///modules/sessionstore/ContentSessionStore.sys.mjs"
   );
 }
 
diff --git a/browser/components/sessionstore/ContentRestore.jsm b/browser/components/sessionstore/ContentRestore.sys.mjs
similarity index 99%
rename from browser/components/sessionstore/ContentRestore.jsm
rename to browser/components/sessionstore/ContentRestore.sys.mjs
index 10762860098e..7caa6dbca1f9 100644
--- a/browser/components/sessionstore/ContentRestore.jsm
+++ b/browser/components/sessionstore/ContentRestore.sys.mjs
@@ -2,16 +2,13 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["ContentRestore"];
-
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
   SessionHistory: "resource://gre/modules/sessionstore/SessionHistory.sys.mjs",
   Utils: "resource://gre/modules/sessionstore/Utils.sys.mjs",
 });
+
 /**
  * This module implements the content side of session restoration. The chrome
  * side is handled by SessionStore.jsm. The functions in this module are called
@@ -41,7 +38,7 @@ ChromeUtils.defineESModuleGetters(lazy, {
  * reset message, which causes resetRestore to be called. At that point it's
  * legal to begin another restore.
  */
-function ContentRestore(chromeGlobal) {
+export function ContentRestore(chromeGlobal) {
   let internal = new ContentRestoreInternal(chromeGlobal);
   let external = {};
 
diff --git a/browser/components/sessionstore/ContentSessionStore.jsm b/browser/components/sessionstore/ContentSessionStore.sys.mjs
similarity index 98%
rename from browser/components/sessionstore/ContentSessionStore.jsm
rename to browser/components/sessionstore/ContentSessionStore.sys.mjs
index e9c5e6569395..7e12a94f036e 100644
--- a/browser/components/sessionstore/ContentSessionStore.jsm
+++ b/browser/components/sessionstore/ContentSessionStore.sys.mjs
@@ -2,16 +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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["ContentSessionStore"];
-
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
-const { clearTimeout, setTimeoutWithTarget } = ChromeUtils.importESModule(
-  "resource://gre/modules/Timer.sys.mjs"
-);
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+import {
+  clearTimeout,
+  setTimeoutWithTarget,
+} from "resource://gre/modules/Timer.sys.mjs";
 
 function debug(msg) {
   Services.console.logStringMessage("SessionStoreContent: " + msg);
@@ -19,12 +14,8 @@ function debug(msg) {
 
 const lazy = {};
 
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "ContentRestore",
-  "resource:///modules/sessionstore/ContentRestore.jsm"
-);
 ChromeUtils.defineESModuleGetters(lazy, {
+  ContentRestore: "resource:///modules/sessionstore/ContentRestore.sys.mjs",
   SessionHistory: "resource://gre/modules/sessionstore/SessionHistory.sys.mjs",
 });
 
@@ -512,7 +503,7 @@ const MESSAGES = [
   "SessionStore:prepareForProcessChange",
 ];
 
-class ContentSessionStore {
+export class ContentSessionStore {
   constructor(mm) {
     if (Services.appinfo.sessionHistoryInParent) {
       throw new Error("This frame script should not be loaded for SHIP");
diff --git a/browser/components/sessionstore/GlobalState.jsm b/browser/components/sessionstore/GlobalState.sys.mjs
similarity index 95%
rename from browser/components/sessionstore/GlobalState.jsm
rename to browser/components/sessionstore/GlobalState.sys.mjs
index d6c1e80a030e..a49fe4650d89 100644
--- a/browser/components/sessionstore/GlobalState.jsm
+++ b/browser/components/sessionstore/GlobalState.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["GlobalState"];
-
 const EXPORTED_METHODS = [
   "getState",
   "clear",
@@ -14,10 +10,11 @@ const EXPORTED_METHODS = [
   "delete",
   "setFromState",
 ];
+
 /**
  * Module that contains global session data.
  */
-function GlobalState() {
+export function GlobalState() {
   let internal = new GlobalStateInternal();
   let external = {};
   for (let method of EXPORTED_METHODS) {
diff --git a/browser/components/sessionstore/RecentlyClosedTabsAndWindowsMenuUtils.jsm b/browser/components/sessionstore/RecentlyClosedTabsAndWindowsMenuUtils.sys.mjs
similarity index 96%
rename from browser/components/sessionstore/RecentlyClosedTabsAndWindowsMenuUtils.jsm
rename to browser/components/sessionstore/RecentlyClosedTabsAndWindowsMenuUtils.sys.mjs
index 241a0b5b827b..9bfb81999f41 100644
--- a/browser/components/sessionstore/RecentlyClosedTabsAndWindowsMenuUtils.jsm
+++ b/browser/components/sessionstore/RecentlyClosedTabsAndWindowsMenuUtils.sys.mjs
@@ -2,30 +2,19 @@
  * 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/. */
 
-var EXPORTED_SYMBOLS = ["RecentlyClosedTabsAndWindowsMenuUtils"];
-
 const lazy = {};
 
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "PluralForm",
-  "resource://gre/modules/PluralForm.jsm"
-);
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "SessionStore",
-  "resource:///modules/sessionstore/SessionStore.jsm"
-);
-
 ChromeUtils.defineESModuleGetters(lazy, {
   PlacesUIUtils: "resource:///modules/PlacesUIUtils.sys.mjs",
+  PluralForm: "resource://gre/modules/PluralForm.sys.mjs",
+  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
 });
 
 var navigatorBundle = Services.strings.createBundle(
   "chrome://browser/locale/browser.properties"
 );
 
-var RecentlyClosedTabsAndWindowsMenuUtils = {
+export var RecentlyClosedTabsAndWindowsMenuUtils = {
   /**
    * Builds up a document fragment of UI items for the recently closed tabs.
    * @param   aWindow
diff --git a/browser/components/sessionstore/RunState.jsm b/browser/components/sessionstore/RunState.sys.mjs
similarity index 97%
rename from browser/components/sessionstore/RunState.jsm
rename to browser/components/sessionstore/RunState.sys.mjs
index 64be1a9b05d7..94f9a86fcddc 100644
--- a/browser/components/sessionstore/RunState.jsm
+++ b/browser/components/sessionstore/RunState.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["RunState"];
-
 const STATE_STOPPED = 0;
 const STATE_RUNNING = 1;
 const STATE_QUITTING = 2;
@@ -21,7 +17,7 @@ var state = STATE_STOPPED;
  * the initial browser window has loaded we switch to STATE_RUNNING. On the
  * first notice that a browser shutdown was granted we switch to STATE_QUITTING.
  */
-var RunState = Object.freeze({
+export var RunState = Object.freeze({
   // If we're stopped then SessionStore hasn't been initialized yet. As soon
   // as the session is read from disk and the initial browser window has loaded
   // the run state will change to STATE_RUNNING.
diff --git a/browser/components/sessionstore/SessionCookies.jsm b/browser/components/sessionstore/SessionCookies.sys.mjs
similarity index 98%
rename from browser/components/sessionstore/SessionCookies.jsm
rename to browser/components/sessionstore/SessionCookies.sys.mjs
index 90a3af5d7e7b..baaa5039c773 100644
--- a/browser/components/sessionstore/SessionCookies.jsm
+++ b/browser/components/sessionstore/SessionCookies.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["SessionCookies"];
-
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
@@ -17,7 +13,7 @@ const MAX_EXPIRY = Number.MAX_SAFE_INTEGER;
 /**
  * The external API implemented by the SessionCookies module.
  */
-var SessionCookies = Object.freeze({
+export var SessionCookies = Object.freeze({
   collect() {
     return SessionCookiesInternal.collect();
   },
diff --git a/browser/components/sessionstore/SessionFile.jsm b/browser/components/sessionstore/SessionFile.sys.mjs
similarity index 97%
rename from browser/components/sessionstore/SessionFile.jsm
rename to browser/components/sessionstore/SessionFile.sys.mjs
index 4e299662116b..b74dbc621c84 100644
--- a/browser/components/sessionstore/SessionFile.jsm
+++ b/browser/components/sessionstore/SessionFile.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["SessionFile"];
-
 /**
  * Implementation of all the disk I/O required by the session store.
  * This is a private API, meant to be used only by the session store.
@@ -19,16 +15,12 @@ var EXPORTED_SYMBOLS = ["SessionFile"];
  * another attempts to copy that file.
  */
 
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
-
 const lazy = {};
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  RunState: "resource:///modules/sessionstore/RunState.jsm",
-  SessionStore: "resource:///modules/sessionstore/SessionStore.jsm",
-  SessionWriter: "resource:///modules/sessionstore/SessionWriter.jsm",
+ChromeUtils.defineESModuleGetters(lazy, {
+  RunState: "resource:///modules/sessionstore/RunState.sys.mjs",
+  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
+  SessionWriter: "resource:///modules/sessionstore/SessionWriter.sys.mjs",
 });
 
 const PREF_UPGRADE_BACKUP = "browser.sessionstore.upgradeBackup.latestBuildID";
@@ -38,7 +30,7 @@ const PREF_MAX_UPGRADE_BACKUPS =
 const PREF_MAX_SERIALIZE_BACK = "browser.sessionstore.max_serialize_back";
 const PREF_MAX_SERIALIZE_FWD = "browser.sessionstore.max_serialize_forward";
 
-var SessionFile = {
+export var SessionFile = {
   /**
    * Read the contents of the session file, asynchronously.
    */
diff --git a/browser/components/sessionstore/SessionMigration.jsm b/browser/components/sessionstore/SessionMigration.sys.mjs
similarity index 97%
rename from browser/components/sessionstore/SessionMigration.jsm
rename to browser/components/sessionstore/SessionMigration.sys.mjs
index 4899d7031c18..26e1e27d5010 100644
--- a/browser/components/sessionstore/SessionMigration.jsm
+++ b/browser/components/sessionstore/SessionMigration.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["SessionMigration"];
-
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
@@ -78,7 +74,7 @@ var SessionMigrationInternal = {
   },
 };
 
-var SessionMigration = {
+export var SessionMigration = {
   /**
    * Migrate a limited set of session data from one path to another.
    */
diff --git a/browser/components/sessionstore/SessionSaver.jsm b/browser/components/sessionstore/SessionSaver.sys.mjs
similarity index 95%
rename from browser/components/sessionstore/SessionSaver.jsm
rename to browser/components/sessionstore/SessionSaver.sys.mjs
index 44ef4422d297..20521bf326bf 100644
--- a/browser/components/sessionstore/SessionSaver.jsm
+++ b/browser/components/sessionstore/SessionSaver.sys.mjs
@@ -2,34 +2,23 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["SessionSaver"];
-
-const {
+import {
   cancelIdleCallback,
   clearTimeout,
   requestIdleCallback,
   setTimeout,
-} = ChromeUtils.importESModule("resource://gre/modules/Timer.sys.mjs");
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
-const { AppConstants } = ChromeUtils.importESModule(
-  "resource://gre/modules/AppConstants.sys.mjs"
-);
+} from "resource://gre/modules/Timer.sys.mjs";
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+import { AppConstants } from "resource://gre/modules/AppConstants.sys.mjs";
 
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
   PrivacyFilter: "resource://gre/modules/sessionstore/PrivacyFilter.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
-});
-
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  RunState: "resource:///modules/sessionstore/RunState.jsm",
-  SessionStore: "resource:///modules/sessionstore/SessionStore.jsm",
-  SessionFile: "resource:///modules/sessionstore/SessionFile.jsm",
+  RunState: "resource:///modules/sessionstore/RunState.sys.mjs",
+  SessionFile: "resource:///modules/sessionstore/SessionFile.sys.mjs",
+  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
 });
 
 /*
@@ -74,7 +63,7 @@ var stopWatchFinish = stopWatch("finish");
 /**
  * The external API implemented by the SessionSaver module.
  */
-var SessionSaver = Object.freeze({
+export var SessionSaver = Object.freeze({
   /**
    * Immediately saves the current session to disk.
    */
diff --git a/browser/components/sessionstore/SessionStartup.jsm b/browser/components/sessionstore/SessionStartup.sys.mjs
similarity index 97%
rename from browser/components/sessionstore/SessionStartup.jsm
rename to browser/components/sessionstore/SessionStartup.sys.mjs
index b8a3441c9731..37d7bf387e96 100644
--- a/browser/components/sessionstore/SessionStartup.jsm
+++ b/browser/components/sessionstore/SessionStartup.sys.mjs
@@ -2,8 +2,6 @@
  * 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/. */
 
-"use strict";
-
 /**
  * Session Storage and Restoration
  *
@@ -29,30 +27,21 @@
  * browser.startup.page is set to 3.
  */
 
-var EXPORTED_SYMBOLS = ["SessionStartup"];
-
 /* :::::::: Constants and Helpers ::::::::::::::: */
 
 const lazy = {};
 
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "SessionFile",
-  "resource:///modules/sessionstore/SessionFile.jsm"
-);
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "StartupPerformance",
-  "resource:///modules/sessionstore/StartupPerformance.jsm"
-);
+ChromeUtils.defineESModuleGetters(lazy, {
+  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
+  SessionFile: "resource:///modules/sessionstore/SessionFile.sys.mjs",
+  StartupPerformance:
+    "resource:///modules/sessionstore/StartupPerformance.sys.mjs",
+});
 ChromeUtils.defineModuleGetter(
   lazy,
   "CrashMonitor",
   "resource://gre/modules/CrashMonitor.jsm"
 );
-ChromeUtils.defineESModuleGetters(lazy, {
-  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
-});
 
 const STATE_RUNNING_STR = "running";
 
@@ -93,7 +82,7 @@ var gOnceInitializedDeferred = (function() {
 
 /* :::::::: The Service ::::::::::::::: */
 
-var SessionStartup = {
+export var SessionStartup = {
   NO_SESSION: TYPE_NO_SESSION,
   RECOVER_SESSION: TYPE_RECOVER_SESSION,
   RESUME_SESSION: TYPE_RESUME_SESSION,
diff --git a/browser/components/sessionstore/SessionStore.jsm b/browser/components/sessionstore/SessionStore.sys.mjs
similarity index 99%
rename from browser/components/sessionstore/SessionStore.jsm
rename to browser/components/sessionstore/SessionStore.sys.mjs
index ed20cffd9ac5..f193eea3e1d2 100644
--- a/browser/components/sessionstore/SessionStore.jsm
+++ b/browser/components/sessionstore/SessionStore.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["SessionStore", "_LastSession"];
-
 // Current version of the format used by Session Restore.
 const FORMAT_VERSION = 1;
 
@@ -217,21 +213,14 @@ const BROWSER_STARTUP_RESUME_SESSION = 3;
 const kNoIndex = Number.MAX_SAFE_INTEGER;
 const kLastIndex = Number.MAX_SAFE_INTEGER - 1;
 
-const { PrivateBrowsingUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/PrivateBrowsingUtils.sys.mjs"
-);
+import { PrivateBrowsingUtils } from "resource://gre/modules/PrivateBrowsingUtils.sys.mjs";
+
 const { TelemetryTimestamps } = ChromeUtils.import(
   "resource://gre/modules/TelemetryTimestamps.jsm"
 );
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
-const { AppConstants } = ChromeUtils.importESModule(
-  "resource://gre/modules/AppConstants.sys.mjs"
-);
-const { GlobalState } = ChromeUtils.import(
-  "resource:///modules/sessionstore/GlobalState.jsm"
-);
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+import { AppConstants } from "resource://gre/modules/AppConstants.sys.mjs";
+import { GlobalState } from "resource:///modules/sessionstore/GlobalState.sys.mjs";
 
 const lazy = {};
 
@@ -244,7 +233,16 @@ ChromeUtils.defineESModuleGetters(lazy, {
   E10SUtils: "resource://gre/modules/E10SUtils.sys.mjs",
   PrivacyFilter: "resource://gre/modules/sessionstore/PrivacyFilter.sys.mjs",
   PromiseUtils: "resource://gre/modules/PromiseUtils.sys.mjs",
+  RunState: "resource:///modules/sessionstore/RunState.sys.mjs",
+  SessionCookies: "resource:///modules/sessionstore/SessionCookies.sys.mjs",
+  SessionFile: "resource:///modules/sessionstore/SessionFile.sys.mjs",
   SessionHistory: "resource://gre/modules/sessionstore/SessionHistory.sys.mjs",
+  SessionSaver: "resource:///modules/sessionstore/SessionSaver.sys.mjs",
+  SessionStartup: "resource:///modules/sessionstore/SessionStartup.sys.mjs",
+  TabAttributes: "resource:///modules/sessionstore/TabAttributes.sys.mjs",
+  TabState: "resource:///modules/sessionstore/TabState.sys.mjs",
+  TabStateCache: "resource:///modules/sessionstore/TabStateCache.sys.mjs",
+  TabStateFlusher: "resource:///modules/sessionstore/TabStateFlusher.sys.mjs",
   setTimeout: "resource://gre/modules/Timer.sys.mjs",
 });
 
@@ -252,16 +250,7 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
   AsyncShutdown: "resource://gre/modules/AsyncShutdown.jsm",
   BrowserWindowTracker: "resource:///modules/BrowserWindowTracker.jsm",
   HomePage: "resource:///modules/HomePage.jsm",
-  RunState: "resource:///modules/sessionstore/RunState.jsm",
-  SessionCookies: "resource:///modules/sessionstore/SessionCookies.jsm",
-  SessionFile: "resource:///modules/sessionstore/SessionFile.jsm",
-  SessionSaver: "resource:///modules/sessionstore/SessionSaver.jsm",
-  SessionStartup: "resource:///modules/sessionstore/SessionStartup.jsm",
-  TabAttributes: "resource:///modules/sessionstore/TabAttributes.jsm",
   TabCrashHandler: "resource:///modules/ContentCrashHandlers.jsm",
-  TabState: "resource:///modules/sessionstore/TabState.jsm",
-  TabStateCache: "resource:///modules/sessionstore/TabStateCache.jsm",
-  TabStateFlusher: "resource:///modules/sessionstore/TabStateFlusher.jsm",
 });
 
 /**
@@ -278,7 +267,7 @@ var gDebuggingEnabled = false;
  */
 var gResistFingerprintingEnabled = false;
 
-var SessionStore = {
+export var SessionStore = {
   get promiseInitialized() {
     return SessionStoreInternal.promiseInitialized;
   },
@@ -6865,4 +6854,4 @@ var LastSession = {
 };
 
 // Exposed for tests
-const _LastSession = LastSession;
+export const _LastSession = LastSession;
diff --git a/browser/components/sessionstore/SessionWriter.jsm b/browser/components/sessionstore/SessionWriter.sys.mjs
similarity index 99%
rename from browser/components/sessionstore/SessionWriter.jsm
rename to browser/components/sessionstore/SessionWriter.sys.mjs
index 942709c2e8da..37f565e4af75 100644
--- a/browser/components/sessionstore/SessionWriter.jsm
+++ b/browser/components/sessionstore/SessionWriter.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["SessionWriter"];
-
 /**
  * We just started (we haven't written anything to disk yet) from
  * `Paths.clean`. The backup directory may not exist.
@@ -53,7 +49,7 @@ function lockIOWithMutex() {
 /**
  * Interface dedicated to handling I/O for Session Store.
  */
-const SessionWriter = {
+export const SessionWriter = {
   init(origin, useOldExtension, paths, prefs = {}) {
     return SessionWriterInternal.init(origin, useOldExtension, paths, prefs);
   },
diff --git a/browser/components/sessionstore/StartupPerformance.jsm b/browser/components/sessionstore/StartupPerformance.sys.mjs
similarity index 98%
rename from browser/components/sessionstore/StartupPerformance.jsm
rename to browser/components/sessionstore/StartupPerformance.sys.mjs
index 7e6ef84494c6..a13333d9d1ee 100644
--- a/browser/components/sessionstore/StartupPerformance.jsm
+++ b/browser/components/sessionstore/StartupPerformance.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["StartupPerformance"];
-
 const lazy = {};
 ChromeUtils.defineESModuleGetters(lazy, {
   clearTimeout: "resource://gre/modules/Timer.sys.mjs",
@@ -19,7 +15,7 @@ const OBSERVED_TOPICS = [
   "sessionstore-initiating-manual-restore",
 ];
 
-var StartupPerformance = {
+export var StartupPerformance = {
   /**
    * Once we have finished restoring initial tabs, we broadcast on this topic.
    */
diff --git a/browser/components/sessionstore/TabAttributes.jsm b/browser/components/sessionstore/TabAttributes.sys.mjs
similarity index 95%
rename from browser/components/sessionstore/TabAttributes.jsm
rename to browser/components/sessionstore/TabAttributes.sys.mjs
index 37a40ca977f4..1c7f54b6abcb 100644
--- a/browser/components/sessionstore/TabAttributes.jsm
+++ b/browser/components/sessionstore/TabAttributes.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["TabAttributes"];
-
 // We never want to directly read or write these attributes.
 // 'image' should not be accessed directly but handled by using the
 //         gBrowser.getIcon()/setIcon() methods.
@@ -22,7 +18,7 @@ const ATTRIBUTES_TO_SKIP = new Set([
 // A set of tab attributes to persist. We will read a given list of tab
 // attributes when collecting tab data and will re-set those attributes when
 // the given tab data is restored to a new tab.
-var TabAttributes = Object.freeze({
+export var TabAttributes = Object.freeze({
   persist(name) {
     return TabAttributesInternal.persist(name);
   },
diff --git a/browser/components/sessionstore/TabState.jsm b/browser/components/sessionstore/TabState.sys.mjs
similarity index 95%
rename from browser/components/sessionstore/TabState.jsm
rename to browser/components/sessionstore/TabState.sys.mjs
index 1fe7ab1c09e9..26f5671c849d 100644
--- a/browser/components/sessionstore/TabState.jsm
+++ b/browser/components/sessionstore/TabState.sys.mjs
@@ -2,30 +2,18 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["TabState"];
-
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
   PrivacyFilter: "resource://gre/modules/sessionstore/PrivacyFilter.sys.mjs",
+  TabAttributes: "resource:///modules/sessionstore/TabAttributes.sys.mjs",
+  TabStateCache: "resource:///modules/sessionstore/TabStateCache.sys.mjs",
 });
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "TabStateCache",
-  "resource:///modules/sessionstore/TabStateCache.jsm"
-);
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "TabAttributes",
-  "resource:///modules/sessionstore/TabAttributes.jsm"
-);
 
 /**
  * Module that contains tab state collection methods.
  */
-var TabState = Object.freeze({
+export var TabState = Object.freeze({
   update(permanentKey, data) {
     TabStateInternal.update(permanentKey, data);
   },
diff --git a/browser/components/sessionstore/TabStateCache.jsm b/browser/components/sessionstore/TabStateCache.sys.mjs
similarity index 98%
rename from browser/components/sessionstore/TabStateCache.jsm
rename to browser/components/sessionstore/TabStateCache.sys.mjs
index 9380ed70b839..81524c4d69cd 100644
--- a/browser/components/sessionstore/TabStateCache.jsm
+++ b/browser/components/sessionstore/TabStateCache.sys.mjs
@@ -2,10 +2,6 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["TabStateCache"];
-
 /**
  * A cache for tabs data.
  *
@@ -16,7 +12,7 @@ var EXPORTED_SYMBOLS = ["TabStateCache"];
  * - that data is used very seldom by SessionStore;
  * - caching private data in addition to public data is memory consuming.
  */
-var TabStateCache = Object.freeze({
+export var TabStateCache = Object.freeze({
   /**
    * Retrieves cached data for a given |tab| or associated |browser|.
    *
diff --git a/browser/components/sessionstore/TabStateFlusher.jsm b/browser/components/sessionstore/TabStateFlusher.sys.mjs
similarity index 97%
rename from browser/components/sessionstore/TabStateFlusher.jsm
rename to browser/components/sessionstore/TabStateFlusher.sys.mjs
index 887f3ab60604..897d02b6f600 100644
--- a/browser/components/sessionstore/TabStateFlusher.jsm
+++ b/browser/components/sessionstore/TabStateFlusher.sys.mjs
@@ -2,16 +2,10 @@
  * 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/. */
 
-"use strict";
-
-var EXPORTED_SYMBOLS = ["TabStateFlusher"];
-
 const lazy = {};
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "SessionStore",
-  "resource:///modules/sessionstore/SessionStore.jsm"
-);
+ChromeUtils.defineESModuleGetters(lazy, {
+  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
+});
 
 /**
  * A module that enables async flushes. Updates from frame scripts are
@@ -20,7 +14,7 @@ ChromeUtils.defineModuleGetter(
  * wait until the frame scripts reported back. At this point the parent has the
  * latest data and the action can continue.
  */
-var TabStateFlusher = Object.freeze({
+export var TabStateFlusher = Object.freeze({
   /**
    * Requests an async flush for the given browser. Returns a promise that will
    * resolve when we heard back from the content process and the parent has
diff --git a/browser/components/sessionstore/content/aboutSessionRestore.js b/browser/components/sessionstore/content/aboutSessionRestore.js
index 9a046cace374..321bb9d0db9e 100644
--- a/browser/components/sessionstore/content/aboutSessionRestore.js
+++ b/browser/components/sessionstore/content/aboutSessionRestore.js
@@ -7,11 +7,9 @@
 const { AppConstants } = ChromeUtils.importESModule(
   "resource://gre/modules/AppConstants.sys.mjs"
 );
-ChromeUtils.defineModuleGetter(
-  this,
-  "SessionStore",
-  "resource:///modules/sessionstore/SessionStore.jsm"
-);
+ChromeUtils.defineESModuleGetters(this, {
+  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
+});
 
 var gStateObject;
 var gTreeData;
diff --git a/browser/components/sessionstore/content/content-sessionStore.js b/browser/components/sessionstore/content/content-sessionStore.js
index 372f875a00a3..a4bdea0bdc46 100644
--- a/browser/components/sessionstore/content/content-sessionStore.js
+++ b/browser/components/sessionstore/content/content-sessionStore.js
@@ -6,8 +6,8 @@
 
 "use strict";
 
-const { ContentSessionStore } = ChromeUtils.import(
-  "resource:///modules/sessionstore/ContentSessionStore.jsm"
+const { ContentSessionStore } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/ContentSessionStore.sys.mjs"
 );
 
 void new ContentSessionStore(this);
diff --git a/browser/components/sessionstore/moz.build b/browser/components/sessionstore/moz.build
index 1b0f43ea0018..d2191375a9b2 100644
--- a/browser/components/sessionstore/moz.build
+++ b/browser/components/sessionstore/moz.build
@@ -10,23 +10,23 @@ BROWSER_CHROME_MANIFESTS += ["test/browser.ini"]
 JAR_MANIFESTS += ["jar.mn"]
 
 EXTRA_JS_MODULES.sessionstore = [
-    "ContentRestore.jsm",
-    "ContentSessionStore.jsm",
-    "GlobalState.jsm",
-    "RecentlyClosedTabsAndWindowsMenuUtils.jsm",
-    "RunState.jsm",
-    "SessionCookies.jsm",
-    "SessionFile.jsm",
-    "SessionMigration.jsm",
-    "SessionSaver.jsm",
-    "SessionStartup.jsm",
-    "SessionStore.jsm",
-    "SessionWriter.jsm",
-    "StartupPerformance.jsm",
-    "TabAttributes.jsm",
-    "TabState.jsm",
-    "TabStateCache.jsm",
-    "TabStateFlusher.jsm",
+    "ContentRestore.sys.mjs",
+    "ContentSessionStore.sys.mjs",
+    "GlobalState.sys.mjs",
+    "RecentlyClosedTabsAndWindowsMenuUtils.sys.mjs",
+    "RunState.sys.mjs",
+    "SessionCookies.sys.mjs",
+    "SessionFile.sys.mjs",
+    "SessionMigration.sys.mjs",
+    "SessionSaver.sys.mjs",
+    "SessionStartup.sys.mjs",
+    "SessionStore.sys.mjs",
+    "SessionWriter.sys.mjs",
+    "StartupPerformance.sys.mjs",
+    "TabAttributes.sys.mjs",
+    "TabState.sys.mjs",
+    "TabStateCache.sys.mjs",
+    "TabStateFlusher.sys.mjs",
 ]
 
 with Files("**"):
diff --git a/browser/components/sessionstore/test/browser_354894_perwindowpb.js b/browser/components/sessionstore/test/browser_354894_perwindowpb.js
index d54355c7cd82..27f822f8ef26 100644
--- a/browser/components/sessionstore/test/browser_354894_perwindowpb.js
+++ b/browser/components/sessionstore/test/browser_354894_perwindowpb.js
@@ -26,8 +26,8 @@
  * notifications. The latter won't.
  */
 
-const { SessionStartup } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionStartup.jsm"
+const { SessionStartup } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionStartup.sys.mjs"
 );
 // The rejection "BrowserWindowTracker.getTopWindow(...) is null" is left
 // unhandled in some cases. This bug should be fixed, but for the moment this
diff --git a/browser/components/sessionstore/test/browser_394759_basic.js b/browser/components/sessionstore/test/browser_394759_basic.js
index d8b16aae7e23..442f04cd0ce2 100644
--- a/browser/components/sessionstore/test/browser_394759_basic.js
+++ b/browser/components/sessionstore/test/browser_394759_basic.js
@@ -8,8 +8,8 @@ const TEST_URL =
   "data:text/html;charset=utf-8,<input%20id=txt>" +
   "<input%20type=checkbox%20id=chk>";
 
-const { SessionStore } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionStore.jsm"
+const { SessionStore } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionStore.sys.mjs"
 );
 
 /**
diff --git a/browser/components/sessionstore/test/browser_461634.js b/browser/components/sessionstore/test/browser_461634.js
index c713e267f07f..5de6b92c330d 100644
--- a/browser/components/sessionstore/test/browser_461634.js
+++ b/browser/components/sessionstore/test/browser_461634.js
@@ -2,8 +2,8 @@
  * 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/. */
 
-const { SessionStore } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionStore.jsm"
+const { SessionStore } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionStore.sys.mjs"
 );
 
 add_task(async function testClosedTabData() {
diff --git a/browser/components/sessionstore/test/browser_closedId.js b/browser/components/sessionstore/test/browser_closedId.js
index 1a362931875e..ade315a8742a 100644
--- a/browser/components/sessionstore/test/browser_closedId.js
+++ b/browser/components/sessionstore/test/browser_closedId.js
@@ -3,8 +3,8 @@
 
 "use strict";
 
-const { SessionStore } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionStore.jsm"
+const { SessionStore } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionStore.sys.mjs"
 );
 const BACKUP_STATE = SessionStore.getBrowserState();
 
diff --git a/browser/components/sessionstore/test/browser_duplicate_history.js b/browser/components/sessionstore/test/browser_duplicate_history.js
index f916ce4b5a5d..9e9a386e3bcf 100644
--- a/browser/components/sessionstore/test/browser_duplicate_history.js
+++ b/browser/components/sessionstore/test/browser_duplicate_history.js
@@ -1,18 +1,7 @@
-ChromeUtils.defineModuleGetter(
-  this,
-  "SessionStore",
-  "resource:///modules/sessionstore/SessionStore.jsm"
-);
-ChromeUtils.defineModuleGetter(
-  this,
-  "TabStateCache",
-  "resource:///modules/sessionstore/TabStateCache.jsm"
-);
-ChromeUtils.defineModuleGetter(
-  this,
-  "TabStateFlusher",
-  "resource:///modules/sessionstore/TabStateFlusher.jsm"
-);
+ChromeUtils.defineESModuleGetters(this, {
+  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
+  TabStateCache: "resource:///modules/sessionstore/TabStateCache.sys.mjs",
+});
 
 add_task(async function() {
   await BrowserTestUtils.withNewTab("http://example.com", async function(
diff --git a/browser/components/sessionstore/test/browser_duplicate_tab_in_new_window.js b/browser/components/sessionstore/test/browser_duplicate_tab_in_new_window.js
index 036b0081c11e..0c7782535657 100644
--- a/browser/components/sessionstore/test/browser_duplicate_tab_in_new_window.js
+++ b/browser/components/sessionstore/test/browser_duplicate_tab_in_new_window.js
@@ -1,8 +1,6 @@
-ChromeUtils.defineModuleGetter(
-  this,
-  "SessionStore",
-  "resource:///modules/sessionstore/SessionStore.jsm"
-);
+ChromeUtils.defineESModuleGetters(this, {
+  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
+});
 
 add_task(async function() {
   await BrowserTestUtils.withNewTab("https://example.com", async function(
diff --git a/browser/components/sessionstore/test/browser_firefoxView_selected_restore.js b/browser/components/sessionstore/test/browser_firefoxView_selected_restore.js
index 3ec073b6ace4..690c748c1052 100644
--- a/browser/components/sessionstore/test/browser_firefoxView_selected_restore.js
+++ b/browser/components/sessionstore/test/browser_firefoxView_selected_restore.js
@@ -1,8 +1,8 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
-const { _LastSession } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionStore.jsm"
+const { _LastSession } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionStore.sys.mjs"
 );
 const { sinon } = ChromeUtils.import("resource://testing-common/Sinon.jsm");
 
diff --git a/browser/components/sessionstore/test/browser_sessionStoreContainer.js b/browser/components/sessionstore/test/browser_sessionStoreContainer.js
index b10f78cfd6d3..ab92a6ba7564 100644
--- a/browser/components/sessionstore/test/browser_sessionStoreContainer.js
+++ b/browser/components/sessionstore/test/browser_sessionStoreContainer.js
@@ -121,10 +121,6 @@ function waitForNewCookie() {
 add_task(async function test() {
   const USER_CONTEXTS = ["default", "personal", "work"];
 
-  const { TabStateFlusher } = ChromeUtils.import(
-    "resource:///modules/sessionstore/TabStateFlusher.jsm"
-  );
-
   // Make sure userContext is enabled.
   await SpecialPowers.pushPrefEnv({
     set: [["privacy.userContext.enabled", true]],
diff --git a/browser/components/sessionstore/test/browser_undoCloseById.js b/browser/components/sessionstore/test/browser_undoCloseById.js
index fa56db3bfaa2..7a513d730ce9 100644
--- a/browser/components/sessionstore/test/browser_undoCloseById.js
+++ b/browser/components/sessionstore/test/browser_undoCloseById.js
@@ -5,8 +5,8 @@
  * This test is for the undoCloseById function.
  */
 
-const { SessionStore } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionStore.jsm"
+const { SessionStore } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionStore.sys.mjs"
 );
 
 async function openWindow(url) {
diff --git a/browser/components/sessionstore/test/head.js b/browser/components/sessionstore/test/head.js
index a3a75cedecea..4150f826c64a 100644
--- a/browser/components/sessionstore/test/head.js
+++ b/browser/components/sessionstore/test/head.js
@@ -20,17 +20,17 @@ const HTTPSROOT = ROOT.replace(
   "https://example.com/"
 );
 
-const { SessionSaver } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionSaver.jsm"
+const { SessionSaver } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionSaver.sys.mjs"
 );
-const { SessionFile } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionFile.jsm"
+const { SessionFile } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionFile.sys.mjs"
 );
-const { TabState } = ChromeUtils.import(
-  "resource:///modules/sessionstore/TabState.jsm"
+const { TabState } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/TabState.sys.mjs"
 );
-const { TabStateFlusher } = ChromeUtils.import(
-  "resource:///modules/sessionstore/TabStateFlusher.jsm"
+const { TabStateFlusher } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/TabStateFlusher.sys.mjs"
 );
 const ss = SessionStore;
 
diff --git a/browser/components/sessionstore/test/unit/head.js b/browser/components/sessionstore/test/unit/head.js
index d7f33990e77e..7217841201b6 100644
--- a/browser/components/sessionstore/test/unit/head.js
+++ b/browser/components/sessionstore/test/unit/head.js
@@ -1,8 +1,6 @@
-ChromeUtils.defineModuleGetter(
-  this,
-  "SessionStartup",
-  "resource:///modules/sessionstore/SessionStartup.jsm"
-);
+ChromeUtils.defineESModuleGetters(this, {
+  SessionStartup: "resource:///modules/sessionstore/SessionStartup.sys.mjs",
+});
 
 // Call a function once initialization of SessionStartup is complete
 function afterSessionStartupInitialization(cb) {
diff --git a/browser/components/sessionstore/test/unit/test_backup_once.js b/browser/components/sessionstore/test/unit/test_backup_once.js
index 4613188c1055..19bb267ef327 100644
--- a/browser/components/sessionstore/test/unit/test_backup_once.js
+++ b/browser/components/sessionstore/test/unit/test_backup_once.js
@@ -3,14 +3,14 @@
 
 "use strict";
 
-const { SessionWriter } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionWriter.jsm"
+const { SessionWriter } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionWriter.sys.mjs"
 );
 
 // Make sure that we have a profile before initializing SessionFile.
 const profd = do_get_profile();
-const { SessionFile } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionFile.jsm"
+const { SessionFile } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionFile.sys.mjs"
 );
 const Paths = SessionFile.Paths;
 
diff --git a/browser/components/sessionstore/test/unit/test_final_write_cleanup.js b/browser/components/sessionstore/test/unit/test_final_write_cleanup.js
index 3660c156c260..5a55f274f5f4 100644
--- a/browser/components/sessionstore/test/unit/test_final_write_cleanup.js
+++ b/browser/components/sessionstore/test/unit/test_final_write_cleanup.js
@@ -7,15 +7,17 @@
  * entries.
  */
 
-const { SessionWriter } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionWriter.jsm"
+const { SessionWriter } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionWriter.sys.mjs"
 );
 
 // Make sure that we have a profile before initializing SessionFile.
 do_get_profile();
 const {
   SessionFile: { Paths },
-} = ChromeUtils.import("resource:///modules/sessionstore/SessionFile.jsm");
+} = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionFile.sys.mjs"
+);
 
 const MAX_ENTRIES = 9;
 const URL = "http://example.com/#";
diff --git a/browser/components/sessionstore/test/unit/test_histogram_corrupt_files.js b/browser/components/sessionstore/test/unit/test_histogram_corrupt_files.js
index d5508add7f66..5cdb8aff9f3f 100644
--- a/browser/components/sessionstore/test/unit/test_histogram_corrupt_files.js
+++ b/browser/components/sessionstore/test/unit/test_histogram_corrupt_files.js
@@ -14,8 +14,8 @@ const HistogramId = "FX_SESSION_RESTORE_ALL_FILES_CORRUPT";
 
 // Prepare the session file.
 do_get_profile();
-const { SessionFile } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionFile.jsm"
+const { SessionFile } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionFile.sys.mjs"
 );
 
 /**
diff --git a/browser/components/sessionstore/test/unit/test_migration_lz4compression.js b/browser/components/sessionstore/test/unit/test_migration_lz4compression.js
index 86ff5ba4b681..7fea3ece204a 100644
--- a/browser/components/sessionstore/test/unit/test_migration_lz4compression.js
+++ b/browser/components/sessionstore/test/unit/test_migration_lz4compression.js
@@ -1,13 +1,13 @@
 "use strict";
 
-const { SessionWriter } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionWriter.jsm"
+const { SessionWriter } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionWriter.sys.mjs"
 );
 
 // Make sure that we have a profile before initializing SessionFile.
 const profd = do_get_profile();
-const { SessionFile } = ChromeUtils.import(
-  "resource:///modules/sessionstore/SessionFile.jsm"
+const { SessionFile } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/SessionFile.sys.mjs"
 );
 const Paths = SessionFile.Paths;
 
diff --git a/browser/components/sessionstore/test/unit/test_startup_invalid_session.js b/browser/components/sessionstore/test/unit/test_startup_invalid_session.js
index 823717677176..50960b1d4310 100644
--- a/browser/components/sessionstore/test/unit/test_startup_invalid_session.js
+++ b/browser/components/sessionstore/test/unit/test_startup_invalid_session.js
@@ -3,8 +3,8 @@
 
 function run_test() {
   let profd = do_get_profile();
-  var SessionFile = ChromeUtils.import(
-    "resource:///modules/sessionstore/SessionFile.jsm"
+  var SessionFile = ChromeUtils.importESModule(
+    "resource:///modules/sessionstore/SessionFile.sys.mjs"
   ).SessionFile;
 
   let sourceSession = do_get_file("data/sessionstore_invalid.js");
diff --git a/browser/components/sessionstore/test/unit/test_startup_session_async.js b/browser/components/sessionstore/test/unit/test_startup_session_async.js
index a8f72b1b3b52..a61c9fe422ec 100644
--- a/browser/components/sessionstore/test/unit/test_startup_session_async.js
+++ b/browser/components/sessionstore/test/unit/test_startup_session_async.js
@@ -8,8 +8,8 @@
 
 function run_test() {
   let profd = do_get_profile();
-  var SessionFile = ChromeUtils.import(
-    "resource:///modules/sessionstore/SessionFile.jsm"
+  var SessionFile = ChromeUtils.importESModule(
+    "resource:///modules/sessionstore/SessionFile.sys.mjs"
   ).SessionFile;
 
   let sourceSession = do_get_file("data/sessionstore_valid.js");
diff --git a/tools/lint/rejected-words.yml b/tools/lint/rejected-words.yml
index abca800c239d..b6b6419a79a4 100644
--- a/tools/lint/rejected-words.yml
+++ b/tools/lint/rejected-words.yml
@@ -62,7 +62,7 @@ avoid-blacklist-and-whitelist:
         - browser/components/preferences/privacy.js
         - browser/components/resistfingerprinting/test/mochitest/test_bug1354633_media_error.html
         - browser/components/safebrowsing/content/test/browser_whitelisted.js
-        - browser/components/sessionstore/ContentSessionStore.jsm
+        - browser/components/sessionstore/ContentSessionStore.sys.mjs
         - browser/components/sessionstore/test/browser_crashedTabs.js
         - browser/components/uitour/UITourChild.jsm
         - browser/components/urlbar/tests/browser/browser_searchSingleWordNotification.js