Under the ~/.mozilla/firefox folder, you can see a profile.ini
file and a folder with a name like 1iy60s8h.default
You can backup these and start Firefox again.You will lose all add-ons, extensions and bookmarks.
Bookmarks can be restored but add-ons and extensions have to be reinstalled.
Start Firefox and a new profiles.ini
file will be created. Also a new folder with a strange name
Check to see if the problem still exists. If not, start reinstalling your add-ons and extensions one by one.
Maybe one of those is causing the problem.
Also, for your bookmarks, go to the old "strange-name-folder" and copy the file bookmarks.html
file to your new "strange-name-folder". This will restore your bookmarks.
Off course there is a much better way
Go to Help -> Troubleshooting options
There you have the option to Reset Firefox.
Remember before proceeding: you will lose all add-ons/extensions currently installed in your browser!
You will have to install them from scratch.
The only thing that Firefox will (try to) keep after the reset is History & Bookmarks, Passwords, Form History and Cookies.
It might be a good idea to backup your bookmarks, though, before proceeding with resetting your Firefox.
This option is similar to deleting your current profile and creating a new one.