Glad it's not just me. All of those really seem to stress Firefox out on my iMac. Chrome is far more efficient with something like Twitch.

Interesting thing I've noticed: If you don't use chat much and just want the video, try using Twitch's "pop-out" player that opens in its own window- for me this uses far less CPU (even in Chrome)

Chrome's "switch to fullscreen" transition on twitch for me is super laggy though, and I haven't been able to solve that one (Firefox switches to fullscreen smoothly).

Yea, most of my browser time spent during free time is strictly on Twitch/Youtube/Netflix. Until these see improvements, then I won't make the switch.

I only use firefox (for privacy reasons). But the macbook-burning-a-hole-in-my-pants behaviour that firefox creates on these sites has led me to using mpv with youtube-dl to watch most of youtube and all of twitch. If you have both installed you can just do a 'mpv https://www.twitch.tv/username' and it will work quite nicely. You might need to set up mpv to get the best quality, I think putting 'ytdl-format=bestvideo+bestaudio/best' in ~/.config/mpv/mpv.conf is sufficient. HTH.

I am also in this camp and want to say that twitch especially is just horrible for performance

Which is so surprising to me because it's using the HTML5 video player and toggling around with hardware acceleration does nothing to fix the issue. Perhaps it's the integrated chat + any of the add ones that Twitch has written for the videos?

I have noticed the pop-out player seems far more efficient, which leads me to think the chat and other things going on around the video might be the culprit

Unrelated, but what do people do on twitch? I worry about getting out of touch with my children.

In addition to FreeFulls comment, there are also talkshows/(video)podcasts. It's basically the main broadcasting platform for gamers and tech people.

Twitch is mostly people streaming video of themselves playing games, but there are also some programmers that stream as they write software.