diff --git a/packages/playwright-core/src/server/browserContext.ts b/packages/playwright-core/src/server/browserContext.ts
index 2eab61d2e1..d75be1c34d 100644
--- a/packages/playwright-core/src/server/browserContext.ts
+++ b/packages/playwright-core/src/server/browserContext.ts
@@ -515,13 +515,15 @@ export abstract class BrowserContext extends SdkObject {
     };
     const originsToSave = new Set(this._origins);
 
+    const collectScript = `(${storageScript.collect})((${utilityScriptSerializers.source})(), ${this._browser.options.name === 'firefox'})`;
+
     // First try collecting storage stage from existing pages.
     for (const page of this.pages()) {
       const origin = page.mainFrame().origin();
       if (!origin || !originsToSave.has(origin))
         continue;
       try {
-        const storage: storageScript.Storage = await page.mainFrame().nonStallingEvaluateInExistingContext(`(${storageScript.collect})((${utilityScriptSerializers.source})())`, 'utility');
+        const storage: storageScript.Storage = await page.mainFrame().nonStallingEvaluateInExistingContext(collectScript, 'utility');
         if (storage.localStorage.length || storage.indexedDB.length)
           result.origins.push({ origin, localStorage: storage.localStorage, indexedDB: storage.indexedDB });
         originsToSave.delete(origin);
@@ -541,7 +543,7 @@ export abstract class BrowserContext extends SdkObject {
       for (const origin of originsToSave) {
         const frame = page.mainFrame();
         await frame.goto(internalMetadata, origin);
-        const storage: Awaited<ReturnType<typeof storageScript.collect>> = await frame.evaluateExpression(`(${storageScript.collect})((${utilityScriptSerializers.source})())`, { world: 'utility' });
+        const storage: storageScript.Storage = await frame.evaluateExpression(collectScript, { world: 'utility' });
         if (storage.localStorage.length || storage.indexedDB.length)
           result.origins.push({ origin, localStorage: storage.localStorage, indexedDB: storage.indexedDB });
       }
diff --git a/packages/playwright-core/src/server/storageScript.ts b/packages/playwright-core/src/server/storageScript.ts
index 0986650acc..25b1ca9324 100644
--- a/packages/playwright-core/src/server/storageScript.ts
+++ b/packages/playwright-core/src/server/storageScript.ts
@@ -19,7 +19,7 @@ import type { source } from './isomorphic/utilityScriptSerializers';
 
 export type Storage = Omit<channels.OriginStorage, 'origin'>;
 
-export async function collect(serializers: ReturnType<typeof source>): Promise<Storage> {
+export async function collect(serializers: ReturnType<typeof source>, isFirefox: boolean): Promise<Storage> {
   const idbResult = await Promise.all((await indexedDB.databases()).map(async dbInfo => {
     if (!dbInfo.name)
       throw new Error('Database name is empty');
@@ -33,11 +33,26 @@ export async function collect(serializers: ReturnType<typeof source>): Promise<S
       });
     }
 
+    function isPlainObject(v: any) {
+      const ctor = v?.constructor;
+      if (ctor === Object)
+        return true;
+
+      // firefox bug. the above check doesn't work in the utility world.
+      if (isFirefox) {
+        const constructorImpl = ctor?.toString();
+        if (constructorImpl.startsWith('function Object() {') && constructorImpl.includes(' [native code]'))
+          return true;
+      }
+
+      return false;
+    }
+
     function trySerialize(value: any): { trivial?: any, encoded?: any } {
       let trivial = true;
       const encoded = serializers.serializeAsCallArgument(value, v => {
         const isTrivial = (
-          v?.constructor === Object
+          isPlainObject(v)
           || Array.isArray(v)
           || typeof v === 'string'
           || typeof v === 'number'