I've also been seeing this in Firefox for the past couple weeks or so.
The video quality will default to "Auto-1080p" or similar but it will be visibly much worse than 1080p quality. Switching to 1080p manually seems to be the only way to get good quality.
I strongly suspect that at least part of the reason for these is to discourage people from using Google's properties with browsers other than Chrome (whether it was the reason for creating them, or just noted as a benefit for refusing to fix them once they were identified).
