YouTube picture-in-picture works on Firefox for Android again
Update to Firefox version 138.0.2

Picture-in-picture (PiP) is one of YouTube's most appealing features. Not only does the feature allow you to keep an eye on your favorite YouTube content while you browse through other areas of your smartphone, it also gives users easy-to-use controls to seamlessly pause, rewind, and skip sections of the video right from the miniplayer.