Lets ignore your hatred for Firefox for a moment. 60FPS is supported by a grand total of 10% of the users of the internet (Chrome's marketshare). The rest of the internet is now forcibly stuck in 480p resolution and below for anything uploaded at 60FPS since there's no 720/30 option.
The other side, this could be a good tactic by Google to get people to use their browser.
I am pretty sure 60 FPS is dependent on HTML5 support. If you have a browser hat supports HTML5 video, you're good to go. Better HMTL5 video support for Firefox is in the works iirc. In fact I think it will be here next release. Also, I do not think you're stuck with 480p if your browser doesnt work well with HTML5 video. I think it just goes down to 30 FPS automatically.