diff --git a/packages/playwright-core/src/server/storageScript.ts b/packages/playwright-core/src/server/storageScript.ts
index 0986650acc296b..45097e2f191f40 100644
--- a/packages/playwright-core/src/server/storageScript.ts
+++ b/packages/playwright-core/src/server/storageScript.ts
@@ -33,11 +33,24 @@ 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. apparently, plain objects returned from IndexedDB don't have the right constructor.
+      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'