Blocked: All third-party storage access requests
A request to access cookies or storage was blocked because it came from a third-party (a different origin) and content blocking is enabled.
Message
Firefox:
CookieBlockedForeign=Request to access cookies or storage on "X" was blocked because we are blocking all third-party storage access requests and content blocking is enabled.
What can be done
The permission can be changed or removed by going to Settings > Privacy & Security > Enhanced Tracking Protection and adding an exception with the Manage Exceptions… button.
If the resource that is being blocked doesn't need authentication, you can fix the warning message by adding a crossorigin="anonymous" attribute to the relevant element.