[shmerl]

I'm using Youtube dark theme with Firefox just fine. But I had to jump through some hoops in their site settings, though without spoofing the user agent.

What doesn't work at all is their Hangounts, because Google are doing something fishy with WebRTC there:

Hangouts video and voice calls don’t work in Firefox for now. Google is working to fix this as soon as possible. Until then, use a different supported browser.

Not to mention the complete mess they caused to XMPP federation by killing Google Talk.

[vram22]

Leaving aside XMPP federation (though that is a good point), killing Google Talk itself was a bad idea. It was very good and useful, both the text chat and the voice calls feature, and Hangouts, its replacement, sucks heavily.

[shmerl]

I'm using neither, but for me the worst thing were cut off XMPP contacts who were on Google Talk (and later Hangouts). I was reaching them through XMPP federation, and Google really messed things up.

[ryukafalz]

Yeah, it was pretty bad - contacts who were "upgraded" to Hangouts just had me disappear from their contact lists, and on my end it looked like they were constantly in "away" status but they never got my messages.

With no announcement of any of this ahead of time.

Complete mess.