The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Thank you for your reply.If I do this,do you know if all the tabs that I currently have open (approximately 80 tabs) will still be available after the reset ??

I have investigated for myself and I WILL NOT use this "solution" as you call it.If this "solution" were used,I would INDEED LOSE ALL of my open tabs and tab groups ! WHY would you tell someone to do this ? If you are not certain how to "help" someone...DO NOT TRY

You can bookmark all open tabs via the right-click context menu of the tab bar to save them in a bookmarks folder.
That way you can restore them after fixing this issue.

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox Profile Folder that store session data.

Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them).

• http://kb.mozillazine.org/Multiple_profile_files_created