I recently had to restore OSX yosemite after updating to El Capitan, El Capitan broke my mail app so I restored to my earlier back up. However this somehow broke firefox so that now when I try to start it I get the message below: Profile Missing Your Firefox profile cannot be loaded. It may be missing or inaccessible. I searched for a solution and found a terminal script : /Applications/Firefox.app/Contents/MacOS/firefox-bin -P However running this returns the same error. I tried several things including installing firefox developer but everything results in the same error. Is there anything I can do, (short of getting a full clean osx install) to fix firefox. It is by far my favorite browser for my work as a website builder. Is there anyway to erase all existing firefox data so that I can get a true fresh install?