Firefox 65.0 high CPU while watching Youtube videos, TOP displays 80%-100%+ CPU use of Web Content
 

This happend on 3 laptops now. I've tried add-on "h264ify" with "block 60fps video" as "on". That seemed to prolong the time a bit before CPU goes crazy high again. I also checked "about: performance" results. Add-ons do not show high nor medium energy impact. Any helpful suggestions are much appreciated.

java scripts? I know sometimes when I have firefox opened and a I don't know how many tabs opened it locks up my laptop. usually when I am actually doing something else like running a script and I have to dump it with a force shut down.

but you say everything looks fine, java scripts would be the only thing left to look into, as far as I know.

here is firefox-65 on youtube, its on slackware current, but it is only using about 25%

i would suggest trying a different browser for youtube, try chromium

Can't see your "web content" running, when you play a youtube video. It should be above firefox in CPU usage. By the way, play the same video for like 10-15 min to get high CPU.

Well, that's not a solution to a problem that I can accept. Loyal firefox user here.

I doubt that would help anyway since Chromium/Chrome use +30% more memory than Firefox.
Try closing youtube then reopen it that speeds up Seamonkey for me when it slows down if not try closing Firefox then start it again.
Youtube is a resource hog.