Overall browser performance seems to be affected. Even high end pc with OCed 8600k struggles with text input fields after few minutes of browsing. This version is not usable, I am thinking about going back to previous one.

If you can replicate this every time I'd look at posting it on bugzilla. https://bugzilla.mozilla.org/home

otherwise, the people who answer questions here, for the most part, are other Firefox users volunteering their time, not Mozilla employees or Firefox developers.

If you want to leave feedback for Firefox developers, you can go to the Firefox Help menu and select Submit Feedback... or use this link. Your feedback gets collected by a team of people who read it and gather data about the most common issues.

You can check the Firefox Task Manager (about:performance) and about:memory pages.

• https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox
• https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-or-cpu-resources

Can you minimize the memory usage via the button on the about:memory page ?

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

GC, CC and minimize memory usage buttons do nothing. I will try playing around with new profile tomorrow but problem is on 2 pcs and even with disabled addons so no idea what could cause it other than this firefox version.

I created new profile. It unloads tabs after closing really slowly but overall in the long run ram usage drops to almost the same as before opening multiple tabs so it is pretty much fine. I guess now I will have to do lots of testing to determine which files from my profile cause this bug :(

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Tried that already. Did not help.

Ok so it looks like I broke my firefox online profile now somehow. I did backup, removed some folders from my profile (containing extensions and skins), firefox started without addons and skins but with bookmarks, passwords etc. Problem with ram still persisted so I closed firefox, removed profile folder and restored backup (I simply archived whole folder to restore it easily). Firefox launched properly and looked like before removing folders - it had add-ons and skins. Unfortunately after few seconds it synced with my profile and removed all add-ons except one and removed skins. So I removed profile folder and restored backup again. And same thing happened - firefox launched with my favourite skin and all add-ons but after few seconds it synced with firefox account and removed all add-ons.

Now I am afraid of launching my second pc connected to this account to not lose my bookmarks.... Any idea how to force my default set-up to be default for firefox profile? No idea why it synced broken state without add-ons and thought it was better one. There is no way to "reject" this sync, except for completely logging out of firefox sync...

Obvious solution would be removing this pc from my account, restoring backup and then syncing this device as new device. But firefox accounts page is so stupid that you can't just remove device from sync. There is only 1 sync state and you cannot choose which you want to use. So if someone removes your bookmarks from 1 pc you cannot choose backup from yesterday to restore them or reject sync to keep them. Ugh.

Now after restoring profile I have to log-in to firefox accounts so I tried to login and quickly enter sync settings and disconnect syncing with keeping profile logged in. It helped, broken settings did not load onto my device. But of course I want to sync especially bookmarks between 2 devices so I enabled it again and it removed add-ons again.

So it looks like firefox synced my broken firefox version without add-ons and thinks this is the only one correct and every time I start browser with restored add-ons it just forcefully removes them. What the hell am I supposed to do now?! How to remove this broken browser state from server? I tried removing all iterations of this pc from my firefox profile (final step logs me out of current state) to leavy only seconds pc on my account. I thought this will think that my correct profile state from yesterday should be loaded. It does nothing - when I log in it just syncs broken profile again.

I want to force firefox to upload my current browser state instead of downloading broken profile state without addons.

It looks like in 2013 there were settings to do it: https://support.mozilla.org/en-US/questions/959980 "select Reset Sync. A window displaying the Sync options will open then Select the action you want to take: Recommended: Merge this computer's data with my Sync data Replace all data on this computer with my Sync data Replace all other devices with this computer's data "

Then I would choose "Replace all other devices with this computer's data" and everything would be fine but of course mozilla had to remove it in the name of simplicity and ruining users experiences...

Update 1: Problem partially fixed by restoring profile, accepting sync changes (which removes my addons) and then restoring 9 folders (attachment) AGAIN. These 9 folders where removed in 1st step which broke my online profile. This somehow adds add-ons to my browser but they are disabled. I can enable them and sync this state as preferred one. However add-ons settings are gone. Greasemonkey scripts, speeddial bookmarks, all gone. I am really annoyed by this firefox behaviour... I guess perfect option would be to restore everything except sync so firefox would keep logged in state and would not download broken profile on 1st launch. No idea which file/folder is responsible for sync state.

Update 2: I restored all folders. It did not help. Then I restored 9 random files (attachment 2). It restored all add-ons but not their settings. Then I pressed sync and they did not disappear! I do not have time to guess which file did it but one of them solved my problem. However my add-ons settings were still missing. So I closed browser and restored whole profile again. After launching browser it was already logged in to sync. I did not have to login again. Only broken thing was theme. Thankfully my theme was in browser so all I had to do was select proper theme. All addons, themes and addons settings were fine and syncing now does not break them.

So solving broken firefox profile was about: 1. Restore whole firefox folder from backup. 2. Enter firefox, confirm password in sync (because it logs you out for some reason). At this step firefox will download broken profile and remove add-ons. 3. Close browser and restore 9 files shown in second attachment. 4. Run firefox again. It should start with restored, enabled add-ons without their settings. 5. Close firefox, restore whole firefox folder again. 6. Run browser. It should not ask for password this time. As this is trusted device it will upload correct browser state into the cloud now. Addons settings should be there too.

Now I can return to trying to find out why the hell is RAM usage broken :|

Did more testing. Issue seems to be related to using only 1 firefox process (which in fact creates 4 processes but... you know ;) ).

Test was about adding 27 websites to bookmarks to easily open them via open all button in bookmark folder menu. Created another clean firefox profile as suggested earlier. Previous clean profile removed.

Test was done slowly, I waited 15-40 seconds each time so cpu and ram usage could stabilise. Both profiles opened mentioned bookmarks multiple times to properly cache them. My ram usage results in GB are as follows:

Clean Firefox profile using 1 process

• 2,4 without browser
• 3,0 with homepage
• 4,7 - 27 bookmarks opened twice + homepage which gives 55 open pages - really high memory usage!
• 3,3 all tabs closed except for homepage. 300 MB of leftovers!
• 5,5 - 55 tabs again (bookmarks opened twice without previously closing browser - same browsing session!)
• 3,6 - all tabs closed again except for homepage. Notice increased ram usage - another 300MB increase over previous measure despite only 1 tab still opened!

All other test were made the same way:

Clean Firefox profile using 8 processes

• 2,4 without browser
• 2,9 with homepage
• 5,0 with 55 tabs - even higher memory usage but 8 processes can explain this
• 3,1 - 54 tabs closed, homepage left
• 5,1 - 54 tabs opened again
• 3,1 - 54 tabs closed, homepage left - ram usage keeps the same despite opening 54 tabs again before. So RAM seems to flush properly and return to previous state!

My Firefox profile using 1 process - my day to day setup, because having 8 processes caused my browser to lag when creating new firefox.exe process each time.

• 2,5 without browser
• 3,1 with homepage
• 3,9 with 55 tabs - notice really low ram usage compared to clean firefox 1 process profile! 3,9GB instead of 4,7GB despite having multiple addons and adblockers which should increase ram usage!
• 3,7 - 54 tabs closed, homepage left - 600MB of leftovers! Much more than in clean firefox!
• 4,3 - 54 tabs opened again. RAM usage higher than before!
• 4,2 - 54 tabs closed, homepage left. Ram pretty much stops flushing at this point. Only 100MB freed from closing 54 tabs!

My Firefox profile set to 8 processes

• 2,5 without browser
• 3,1 with homepage
• 4,1 with 55 tabs - higher than with 1 process but there are 8 processes so this seems normal
• 3,2 - 54 tabs closed, homepage left. Pretty much great result. Almost the same as before opening tabs!
• 4,2 - 54 tabs opened again. Slightly higer ram usage than before
• 3,2 - 54 tabs closed, homepage left. ram usage seems normal
• I did 2 more repeats on this try:
• 4,5 - 54 tabs opened for the third time. RAM usage even higher than before. 400 MB more than in first try!
• 3,4 - RAM usage starts to not flush properly.
• 5,0 - Extreme repeat with 81 new tabs open (82 tabs total)
• 3,6 - 81 tabs closed, homepage left. 500MB of leftovers compared to launch with homepage.

Conclusion from this test is unclear. Something is wrong with this firefox version. My firefox profile also seems to act weird. Why is ram usage in my huge profile with 1 process much lower than in clear firefox but tends to stay the same after closing tabs? Why having multiple processes makes firefox handle ram usage better? It was working fine in 77.0.1

It is likely that the memory use gets fragmented with only one process that makes it impossible to free up all memory. With more content process you can close a content process to cleanly free up all memory used by this content process what isn't possible with one content process that shares all memory. The more memory processes the more tabs can be opened without reusing an already used content process. What matters in this case what tabs share its content process with the homepage if you keep this tab open. Maybe do a test where you close all tabs and prevent Firefox from closing or open a new window.

• about:config => browser.tabs.closeWindowWithLastTab = false

Well apparently you can't even downgrade now. Great. https://support.mozilla.org/en-US/kb/install-older-version-of-firefox

I did what you asked. I did basic test on my profile with 8 processes.

• 4,0GB of ram usage with only facebook opened.
• Then opened few tabs, ram usage goes to 5-6GB.
• I close all of them except for facebook. Ram usage is 4,5GB now (so 500MB excess).
• I close and reopen facebook page without closing browser window - 4,0GB like on clean start!

Then I did test with google as homepage and 8 processes:

• 3,2GB of ram usage with only google opened
• 5,5 after opening same group of tabs
• 3,6 after closing them except for google homepage
• 5,3 after reopening them (less than before!)
• 3,7 after closing them except for google homepage
• 5,8 after reopening them (higher than in first run)
• 4,0 after closing them except for google homepage
• 3,6 after closing google homepage, only empty speed-dial opens - higher than before opening tabs (3,2GB) but still decent score

Then I did test with google as homepage and 1 process. This is where fun starts!

• 3,1GB of ram usage with only google opened
• 5,0 after opening same group of tabs
• 3 jumps up to 5,3 then drop to 4,9 after closing them except for google homepage - terrible score + strange behaviours with ram usage being higher after closing tabs. Maybe some garbage collection processes which do nothing and do not reduce memory usage?
• 6,0 - 6,4 GB after reopening them. Ram usage and cpu usage unable to stabilise, constantly going up and down, even after few minutes. Charts looked like saw (screenshot attached).
• 5,9 after closing them except for google homepage - so pretty much all opened tabs remained in memory
• I did not continue experiment at this point and did not open tabs for 3rd time. Instead I closed google.pl page
• 3,5 after closing google page!!! Looks like all opened tabs were stacked together with this 1 tab in memory!!! It is still much higher than on clean browser (3,1GB) but wow. 2,4GB restored by closing single tab...

Got 78.0.2 update, did not help.

Ok so I think I've found partial solution. Problem is that firefox 78 does not like "disconnect" add-on.

Firefox ram usage in 77.0.1 with all add-ons enabled:

• 550 after launch with 1 tab
• 2270 after opening 39 more tabs (40 tabs in total)
• increase to 2570 then drop to 1020 after closing 39 tabs

Firefox ram usage in 78 and 78.0.1 with all add-ons enabled:

• 530 after launch with 1 tab
• 2350 after opening 39 more tabs
• increase to 2650 then drop to 2090 after closing 39 tabs - stuck at this value forever. Twice the ram usage as in 77!

Firefox ram usage in 78 and 78.0.1 with all add-ons enabled except for disconnect add-on:

• 530 after launch with 1 tab
• 2250 after opening 39 more tabs
• 1070 after closing 39 tabs

As you can see ram usage without disconnect is very similiar to 77. All tests were made with only 1 firefox process set in settings - which in fact creates 4 processes (or 3 in safe mode).

Disconnect add-on seems to be really old, last update was 22.07.2019: https://addons.mozilla.org/pl/firefox/addon/disconnect/

I am not sure what in firefox 78 changed that made this add-on work so bad. I have no idea how to contact developers of firefox. I will also try to inform disconnect on this issue.

I cannot call it complete success because ram usage after closing tabs is still twice as before opening them. However I tested safe mode both in firefox 77 and 78 and it was about 350MB with 1 tab, 1400-1700MB with 40 tabs, 620-690MB after closing 39 tabs. So even clean firefox has issues clearing RAM. I gues this started many versions ago so I am unable to pinpoint exact firefox version unfortunately.

It looks like they promise to fix this issue in latest 78.0.1 !!! https://www.mozilla.org/en-US/firefox/81.0.1/releasenotes/

"Fixed high memory growth with add-ons such as Disconnect installed, causing browser responsiveness issues over time (bug 1658571)"

Update: did some testing. Disconnect does not longer seem to cause memory usage to stay high. For example my overall system memory usage is 3.4GB after browser starts with 2 tabs, 4.7-5.2GB after opening 37 tabs from bookmarks and ~4.2GB after closing all tabs but one. It does not matter if disconnect is enabled or not. Problem fixed I guess? My only wish is for ram usage to drop closer to initial 3.4GB after closing all tabs, except for being stuck at 4.2GB but I guess it is somewhat normal...