It might help others with the same problem. When you figure out what's causing your issues, please let us know. To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.
If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. When the Firefox Safe Mode window appears, select "Start in Safe Mode". (you may need to specify the Firefox installation path e.g.
On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode. On Mac: Hold the option key while starting Firefox. On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut. If Firefox is not running, you can start Firefox in Safe Mode as follows: In previous Firefox versions, click on the Firefox button at the top left of the Firefox window and click on Help (or click on Help in the Menu bar, if you don't have a Firefox button) then click on Restart with Add-ons Disabled. In Firefox 29.0 and above, click the menu button, click Help and select Restart with Add-ons Disabled. If Firefox is open, you can restart in Firefox Safe Mode from the Help menu: Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). Try Firefox Safe Mode to see if the problem goes away.