FireFox is going to be upgraded to TubeShift Extension 0.0.15.0 which is an experimental release to validate the new server implementation is working correctly before it goes out to all the browsers. There are not any expected issues but it is being called an experiment for a reason.
May 27, 2021 Update: The experiment was a success and version 0.0.15.1 is going out to all users. FireFox and Brave/Chrome are already updated. Microsoft will likely catch up with Edge in a few days.