Ugh, @TeamYouTube. Now subtitle editing "magically" broke in Firefox, while it works in Chrome. Just after end screen cards broke in FF and Edge Chromium was blocked from the modern YT view. Intentional or not, can you please stop this?
Firefox is the fastest browser out there but the mobile version sucks. And lack of proper Google API support makes it hard to use. I am currently loving Edge Chromium. Both on mobile and PC and everything works fine here.