YSK: You can install an extension on Firefox (android) that allows you to play YouTube videos with your screen locked: (perfect for listening to obscure music)
It can be a bit buggy at times, but when it comes to just playing music with the screen locked, it's perfect.
Edit: I forgot to also mention that ad blocker extensions make sailing the seas on mobile much more manageable. Extentions, in general, have been a really nice addition.
Yeah. For me the video stops when I lock the screen (or change apps) but I can then press play again on the lock screen (or in the drop down notifications when changed to another app).