diff --git a/apps/browser/src/background/main.background.ts b/apps/browser/src/background/main.background.ts
index 4ddbf73088..8db80f6f2b 100644
--- a/apps/browser/src/background/main.background.ts
+++ b/apps/browser/src/background/main.background.ts
@@ -364,9 +364,10 @@ export default class MainBackground {
     const logoutCallback = async (expired: boolean, userId?: UserId) =>
       await this.logout(expired, userId);
 
-    this.messagingService = this.popupOnlyContext
-      ? new BrowserMessagingPrivateModeBackgroundService()
-      : new BrowserMessagingService();
+    this.messagingService =
+      this.isPrivateMode && BrowserApi.isManifestVersion(2)
+        ? new BrowserMessagingPrivateModeBackgroundService()
+        : new BrowserMessagingService();
     this.logService = new ConsoleLogService(false);
     this.cryptoFunctionService = new WebCryptoFunctionService(self);
     this.keyGenerationService = new KeyGenerationService(this.cryptoFunctionService);
@@ -408,13 +409,14 @@ export default class MainBackground {
       storageServiceProvider,
     );
 
-    this.encryptService = flagEnabled("multithreadDecryption")
-      ? new MultithreadEncryptServiceImplementation(
-          this.cryptoFunctionService,
-          this.logService,
-          true,
-        )
-      : new EncryptServiceImplementation(this.cryptoFunctionService, this.logService, true);
+    this.encryptService =
+      flagEnabled("multithreadDecryption") && BrowserApi.isManifestVersion(2)
+        ? new MultithreadEncryptServiceImplementation(
+            this.cryptoFunctionService,
+            this.logService,
+            true,
+          )
+        : new EncryptServiceImplementation(this.cryptoFunctionService, this.logService, true);
 
     this.singleUserStateProvider = new DefaultSingleUserStateProvider(
       storageServiceProvider,
@@ -558,10 +560,13 @@ export default class MainBackground {
     const backgroundMessagingService = new (class extends MessagingServiceAbstraction {
       // AuthService should send the messages to the background not popup.
       send = (subscriber: string, arg: any = {}) => {
+        if (BrowserApi.isManifestVersion(3)) {
+          that.messagingService.send(subscriber, arg);
+          return;
+        }
+
         const message = Object.assign({}, { command: subscriber }, arg);
-        // FIXME: Verify that this floating promise is intentional. If it is, add an explanatory comment and ensure there is proper error handling.
-        // eslint-disable-next-line @typescript-eslint/no-floating-promises
-        that.runtimeBackground.processMessage(message, that as any);
+        void that.runtimeBackground.processMessage(message, that as any);
       };
     })();
 
diff --git a/apps/browser/src/platform/decorators/session-sync-observable/session-syncer.ts b/apps/browser/src/platform/decorators/session-sync-observable/session-syncer.ts
index 692e33bcce..6561d5074c 100644
--- a/apps/browser/src/platform/decorators/session-sync-observable/session-syncer.ts
+++ b/apps/browser/src/platform/decorators/session-sync-observable/session-syncer.ts
@@ -93,6 +93,10 @@ export class SessionSyncer {
   }
 
   async update(serializedValue: any) {
+    if (!serializedValue) {
+      return;
+    }
+
     const unBuiltValue = JSON.parse(serializedValue);
     if (!BrowserApi.isManifestVersion(3) && BrowserApi.isBackgroundPage(self)) {
       await this.memoryStorageService.save(this.metaData.sessionKey, serializedValue);
@@ -104,6 +108,10 @@ export class SessionSyncer {
   }
 
   private async updateSession(value: any) {
+    if (!value) {
+      return;
+    }
+
     const serializedValue = JSON.stringify(value);
     if (BrowserApi.isManifestVersion(3) || BrowserApi.isBackgroundPage(self)) {
       await this.memoryStorageService.save(this.metaData.sessionKey, serializedValue);
diff --git a/apps/browser/src/popup/services/services.module.ts b/apps/browser/src/popup/services/services.module.ts
index 39b827827b..40daf1b04d 100644
--- a/apps/browser/src/popup/services/services.module.ts
+++ b/apps/browser/src/popup/services/services.module.ts
@@ -62,6 +62,7 @@ import { StateService as BaseStateServiceAbstraction } from "@bitwarden/common/p
 import {
   AbstractMemoryStorageService,
   AbstractStorageService,
+  ObservableStorageService,
 } from "@bitwarden/common/platform/abstractions/storage.service";
 import { StateFactory } from "@bitwarden/common/platform/factories/state-factory";
 import { GlobalState } from "@bitwarden/common/platform/models/domain/global-state";
@@ -157,7 +158,7 @@ const safeProviders: SafeProvider[] = [
   safeProvider({
     provide: MessagingService,
     useFactory: () => {
-      return needsBackgroundInit
+      return needsBackgroundInit && BrowserApi.isManifestVersion(2)
         ? new BrowserMessagingPrivateModePopupService()
         : new BrowserMessagingService();
     },
@@ -369,7 +370,15 @@ const safeProviders: SafeProvider[] = [
   }),
   safeProvider({
     provide: OBSERVABLE_MEMORY_STORAGE,
-    useClass: ForegroundMemoryStorageService,
+    useFactory: () => {
+      if (BrowserApi.isManifestVersion(2)) {
+        return new ForegroundMemoryStorageService();
+      }
+
+      return getBgService<AbstractStorageService & ObservableStorageService>(
+        "memoryStorageForStateProviders",
+      )();
+    },
     deps: [],
   }),
   safeProvider({