Hi, this might be an extension issue, so try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem. Thank you!

You may have corrupt sessionstore file(s).

Type about:support in the address bar and press enter.

Under the page logo on the left side you will see Application Basics. Under this find Profile Folder. To it’s right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Locate the sessionstore file(s). Then rename or delete them. Restart Firefox.

In case you use "Clear history when Firefox closes" then try to disable this feature or at least exclude the history.

FredMcD said

You may have corrupt sessionstore file(s). Type about:support in the address bar and press enter. Under the page logo on the left side you will see Application Basics. Under this find Profile Folder. To it’s right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox. Locate the sessionstore file(s). Then rename or delete them. Restart Firefox.

Tried it. The problem remains.

cor-el said

In case you use "Clear history when Firefox closes" then try to disable this feature or at least exclude the history.

Nope, I do not have that option enabled.

Scribe said

Hi, this might be an extension issue, so try Firefox Safe Mode to see if the problem goes away.

I tried this a few times and when I did exit from safe mode, it did not produce an error the next time. But, at the same time I did exit from a normal instance too, and it was okay the next time.

So, I don't understand.

It could be a corrupt file was overwritten.

Could the problem be the new Tab Groups add-on ? I began using it because I absolutely need it; this was one of the features of firefox that has prevented me from ever using chrome.

I have attached what it says in its preferences page.

Is that the problem?