Hi, I'm sorry to hear that. I checked and on my devices (Firefox 123.0; macOS & Firefox 123.0 Android) and it seems that it's still working. Do you get some errors (ex: popups) when playing the video or it just remains blank? If you find something that can be useful for solving it please open an issue to the GitHub project page (https://github.com/Dinoosauro/youtube-fullscreen-fit) so that I can have a look and improve the extension. Thanks for reporting!