On a system with problematic or malicious add-ons installed, Firefox may open with a blank or transparent window and with no interface elements visible. In some instances Firefox may also crash. This article describes how to resolve the problem.
Make sure that no other instance of Firefox is running or no other Firefox window is open.
You can then start Firefox in Safe Mode by holding down the shift key while starting Firefox.holding down the option key while starting Firefox.going to your Terminal and running:
You may need to specify the Firefox installation path (e.g. /usr/lib/firefox)
Now click on the Start in Safe Mode button in order to run Firefox with extensions and themes disabled for this session.
Click the menu button and choose Add-ons. The Add-ons Manager tab will open.
After completing the above steps, check your computer for malware. See How do I get rid of malware? for some recommended malware removal programs.