Bug 1483765 - Fix the image cache key computation logic to only consider first-party storage access for third-party windows; r=smaug

image/ImageCacheKey.cpp

@@ -141,10 +141,11 @@ ImageCacheKey::GetSpecialCaseDocumentToken(nsIDocument* aDocument, nsIURI* aURI)
     return aDocument;
   }
 
-  // If we must disable the storage, we want to create a unique cache key for
-  // this image.
-  if (nsContentUtils::StorageDisabledByAntiTracking(aDocument, aURI)) {
-    return aDocument;
+  // If the window is 3rd party resource, let's see if first-party storage
+  // access is granted for this image.
+  if (nsContentUtils::IsTrackingResourceWindow(aDocument->GetInnerWindow())) {
+    return nsContentUtils::StorageDisabledByAntiTracking(aDocument, aURI) ?
+             aDocument : nullptr;
   }
 
   // Another scenario is if this image is a 3rd party resource loaded by a