Enter about:support in the URL bar and examine the Graphics section. There should be Webrender in the first row.

Hi,

Thanks for the reply.

Yes webrender is there in the first row.

You posted with a Firefox beta release (81).

Does this also happen with the Firefox 80 release with a new clean profile and with hardware acceleration possibly disabled ?

Hello!

After digging into the CPU usage indepth, it turns out that it wasn't firefox at all... it was malwarebytes!

As soon as I closed MB, bam, firefox works flawlessly again.

Thanks for the help!

Hello! After digging into the CPU usage indepth, it turns out that it wasn't firefox at all... it was malwarebytes! As soon as I closed MB, bam, firefox works flawlessly again. Thanks for the help!

I'm having the exact same issue, and I don't have Malwarebytes on my computer. Took one further step of uninstalling all anti-malware from my computer, and I'm still having this problem. And the first line in my graphics section is "Basic," if that helps.

I've been having this problem, and I've done everything the OP has done, and taking the extra step of uninstalling all anti-malware to see if it was causing the issue. Restarted in safe mode, and the issue was still present, just not quite as bad. It's getting stale. And, at least in my case, it's clearly not anti-malware causing the issue.

Experiencing the same problem, though, I do know for a fact that it is a firefox issue that I can't even get to revert. What I found odd was the fact that it happened when I did my monthly laptop driver update, and it is quite difficult to revert a driver update. The worst part is the fact that Edge and Chrome are just fine and Firefox is the only thing affected.

Not really sure why Firefox seems to be the instigator for high CPU usage, but it is, it's enough to make me use Chrome, very reluctantly. I've noticed that two things generally stop it.

Disable Avast anti-virus (right click the icon in the task tray > Avast Shield Controls > Disable for 1 hour). See if it helps. Other anti-virus software may have the same effect, dunno.

The other one is Adobe software, which is essentially malware for Windows, and they're well aware that their paying customers are having this problem, but have done ZERO over the years to stop it. Open your task manager, kill Adobe Genuine Check, Adobe Update (anything), and Notification.exe. These are all set to autorun, no matter what you do.

You can also get the free app Autoruns.exe from Microsoft to see what's actually running at login, although this won't help you with Adobe, their lame software reinstalls clones of itself, if you kill them in the start up. Windows > Settings > Startup Apps is completely useless placeboware.

My CPU goes from 100% down to about 5% killing these.

I am having the same CPU issue. Suddenly, my computer will get incredibly slow when on a website. I'll check my task manager and Firefox is always at or near 100%. It's incredibly frustrating and I've tried everything here but to no avail. I've used Firefox for years and never had this issue and I find I'm having to switch to Chrome to effectively look for things on the internet when this happens.

Did anyone figure this out?