Earlier quoted context omitted.
They break them on purpose so people will switch to Chrome. And the worst part is, there's no evidence (yet?) that there's malice behind it. Maybe we'll get a whistleblower at some point, but that'll only happen when their income no longer covers buying off their conscience.
What exactly is broken in Firefox on YouTube or Gmail? I'm not a heavy Firefox user, but when I try it every once in a while, I've never noticed anything broken on any of the Google's sites, even Maps and Docs worked just fine - but then, maybe I wasn't trying out some advanced features.
Firefox is the only browser we use and we watch Youtube every day. If it broke, I'd know about it or hear about it.
It never breaks.