《UPDATE #2》
I believe I have discovered the issue! So, as stated in the 1ˢᵗ 2 reviews below, the app works on SOME videos {+5☆}, but on OTHERS it gets cut off as the page reloads {-4☆}.
After some experimentation, I can now definitely confirm that this extension functions EXACTLY as advertised on any "normal" video/playlist (like when listening to a podcast, for example).
HOWEVER, for any video YouTube has flagged as MUSIC, it forces the browser to kill the tab, automatically reloading it when next you switch over to it.

SO THERE YOU HAVE IT, MY DEAR SWEET DEV-TEAM! I've officially located the issue for you. NOW, all you gotta do is fix it.

As for my review... since I've proven the Extension still has ~50% functionality... {+2☆}, bringing the current total up to a respectable 3☆.
That said, should you release an update solving the music issue, I'll GLADLY bumb that badboy back up to 5☆!

Lookin' forward to it.

《UPDATE #1》
Not sure what happened, or if it's just on certain videos, but it definitely started failing every 5-10 minutes...
As soon as you fix that issue, I'll change it back to 5☆ though!
(it's so weird, cuz it literally just worked like 14 hours ago...)

《ORIGINAL REVIEW》
Perfection. It does EXACTLY whst it says it'll do. YouTube/Mozilla keep putting out updates that makes it harder and harder to multitask or listen to videos, but THIS is the solution.
THANK YOU.