What sites? I haven't run into any that Firefox doesn't work with except maybe some sites that wouldn't be useful day-to-day anyway. Not in 10 years or so.
I found several AI sites that seem to block Firefox. Google search labs, the new Bing search. There was also some code collaboration site (duck something) recently. Nothing too too bad but I am finding them more and more.
You know what's the common thing all your examples have in common. They're run by Google. They've been doing this anticompetitive thing for years, deliberately slowing their sites on non chromium browsers, and the senators are turning a blind eye on the same thing that made Bill Gates shit his pants 20 years ago.