1.Try reducing the number of add-ons on the browser. click the three lines on the top right side, scroll down to add-ons, then click the add-on to remove. 2.Try running few applications in your PC. Look on the task manager by right clicking on the taskbar to end non-useful processes. 3.Try running less tabs especially on windows. 4.Check PC for viruses or any malwares that might slow some applications down. 5.Try restarting your PC. The last option i would give is to format your PC.

https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-ram

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

https://support.mozilla.org/en-US/kb/firefox-takes-long-time-start-up

https://support.mozilla.org/en-US/kb/quick-fixes-if-your-firefox-slows-down

MemTest LAST UPDATED : 12/04/2020 Could you please run a tool from http://memtest.org/ in order to check the integrity of your RAM?

You will need a thumb or disk drive to install it on.

Do you let Windows handle the page file or did you set a fixed size ? If you use a fixed size for the page file then try the former and let Windows handle the page file.

Thanks for these suggestions. I'm still working my way through the links. So far I'm not finding anything that rings true in my case. I'm not experiencing any slowdowns or other apparently memory issues with other programs, including another browser (Chrome). I don't have many plug-ins, I have no themes, and I don't keep many tabs open. Also, since posting my original message, I used Firefox's own task manager and discovered that all my plug-ins and open tabs *combined* are using about 150 MB of memory, which is a minuscule proportion of what Windows Task Manager tells me Firefox as a whole is using. Not sure what Safe Mode could tell me that would help me going forward, if it's one of Firefox's many processes/features accounting for the problem.

https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). If the problem goes away, that tells us one thing. If it does not, that tells us something else.

Update: Before trying Safe mode, I restarted Firefox in regular mode. Its memory use, according to Windows Task Manager, promptly dropped from 3.5-5.0 GB to 600 MB. (If I had done this in Safe mode, I would have attributed the drastic reduction to that!) After an hour of moderate (non-video) browsing, it climbed back to 1.4 GB. After another few hours -- same number of tabs open, same (limited) number of add-ons -- it was at 2.4 GB. Before long I expect it to be back to using so much memory that I experience slower performance again. (Point of reference: Chrome has stayed steady at ~ 350 MB this whole time.)

I suppose it's possible that memory use would have dropped a little more if I had restarted in Safe mode -- or would have taken a little longer to climb back up. I may yet try that experiment. (It's a bit of a pain for me to keep restarting because, for privacy reasons, I set my browsers to delete all cookies on restart.) But I'm doubtful that it will help much and in any case using Safe mode long term isn't feasible for me.

Isn't what I'm experiencing -- and I have to assume it's not just me -- called "memory leak"? Do the engineers working on updates know how bad it's gotten?