Take a look in Firefox's Task Manager:

3-bar Menu button -> More -> Task Manager

to help see what is causing these CPU "spikes"

RobertJ said

Take a look in Firefox's Task Manager: 3-bar Menu button -> More -> Task Manager to help see what is causing these CPU "spikes"

The highest "energy impact" task i have is a tab of "medium (9.5)" and is just a youtube tab.

Sometimes, the CPU usage is too high. Sometimes, 90% of my video cache can be cleaned up, or you can restart the browser. If it doesn't work out, you can download the Firefox repair tool. It's very simple

i have OSX FireFox 75.0 in Mavericks 10.9.5 High CPU load with YouTube...

its weird, because playing 2 Tabs or more has No CPU load, BUT... sometimes, 1 tab eats the CPU...

i dont remember that happening in 74.x

FireFoxCP Web Content in Activity Monitor "OSX Task Manager"

The past week or so I've been having a lot of issues with 100% CPU utilization. Culprits seem to be Firefox, Avast, and backup software. I always have tons of Firefox windows and tabs open, and it normally doesn't cause this kind of problem; Today it's been happening with only a few firefox windows open, but they are the processes that are taking up most of the CPU (except when the backup was running, then that was taking up 79-80%).

I've just uninstalled Avast, need to reboot and install Bit Defender, see if that helps.

I will also try running the firefox task manager, which I never heard of before. Not sure where to get the repair tool.

Update: In my case, my laptop was overheating and then dropping down to an unacceptably low processor speed, causing processing tasks to back up. I opened up the case and cleaned out all of the dirt from the fans, and haven't had a problem since.

Noticed in past month or so very high (up to 100%) CPU usage and abnormally high RAM use (approaching 70% with 32GB total and only Firefox Open). Firefox is clearly the offender because stopping Firefox quickly returns CPU usage to mostly idle and CPU usage immediately jumps way up when restarting Firefox. This was not previously a problem so something changed with Firefox. Very annoying because computer becomes very sluggish when Firefox active. Ran comprehensive scans with eset and Malwarebytes and both come up clean.

Tried a refresh but now cannot make new tabs open in custom URL (Google). WTF? Used to be able to specify a custom URL for new tabs but it no longer exists! Plugin now available to do this warns about all the data about my computer usage it will phone home with so not sure why anyone would want to install it.

Have tried searching for solutions but, although these now seem like common problems, no useful solutions available.

Interestingly noticed similar problem with very high CPU usage when open Internet Explorer. Need Explorer at times instead of Firefox because Firefox does not play well or not all with Bureau of Labor Statistics web site. Also never had this problem with IE so what gives?

Tempted to try Google Chrome but reports of all the data it phones home with scare me away from it.

Clear help to solve these problems would be sincerely appreciated.

You can try other browsers. If the usage of cup is still very high, there are several possibilities 1. Check whether your computer driver is installed or updated to the latest version 2. Check your computer for viruses with antivirus software 3. A large part of it may be that the browser is not compatible with your software 4. Open Firefox's own task manager (where to set more options) 5. If the above does not solve your problem, contact me and I can help you solve it remotely

I have similar problem occasionally with sites i load from Google search. As most of places i go i know very well and i'm sure there are no "weird" things embedded in their code, sometimes i do find pages that make my CPU work so hard that i can hear very loud fan spinning -- and on i7, 6-core machine, with latest Windows and lots of resources it is just weird -- especially if comes to "respectful" sites at first glance, like just now watched https://www.laptopmag.com/best-tablets that made my CPU hot again, and weirdest thing, it is just going and going, not like there was some difficult stuff to render on screen, but more like some process that is continuously using processing power... I tried "Prevent accessibility services from accessing your browser" option which worked to some extend, and lots of testing anti-mining and privacy extensions -- with different luck, but i didnt find any reliable solution so far preventing sites loading code that is causing high CPU load.

I am not web designer and i have no idea what kind of stuff can actually make my CPU work more than it should for normal web reading. And it is i believe only Firefox thing, because i just loaded https://www.laptopmag.com/best-tablets into Edge and its all normal, CPU is just like it should, near 0%...

Frank

I opened Task Manager and "Electoral Vote" is at the top of the list. But I have at least four "Electoral Vote" tabs open (each on a different web page, of course). IWBN if I could right-click (contol-click) on a Task Manager line and it would take me to the actual tab, or had some other way of identifying which of several identically-named tabs is the problem.

I have the same problem, but only when I open facebook.

Using task manager I can further confirm that facebook is the problem, the "Facebook (Tab)" task spikes in Energy Impact and memory. When I close the tab everything goes back to normal.