We are aware of an issue that is preventing some browsers, such as Firefox and Vivaldi, from loading games properly. We have identified that this is caused by ad-blocking scripts that are available to those browsers. We have confirmed that disabling ad-blockers should allow games to load properly again, and that the ad-blockers available for Chrome do not seem to be causing the same issues.
If you are experiencing trouble loading a game, we recommend disabling any ad-blockers you may be running until we can investigate a solution for this issue.