1. Possibly unlikely on a Mac but do you have security or other third party software likely to interfere.
   • firefox will not start
2. Save any profiles you do have because they contain passwords and bookmarks
   • see backing up your information
   • do that with all profiles if you have more than one created
3. do a clean reinstall and start that if necessary in safe mode
   • basic troubleshooting scroll the article

Thanks for your reply, but I don't think you understand the issue.

1. My security program isn't the issue.

2. There are no profiles to save. No profiles exist on my computer.

3. I can't start Firefox in Safe Mode because I can't start Firefox at all.

1. My security program isn't the issue.
   • maybe that is correct, or alternatively even a lack of security ! but what do you use ?
     Firewalls, AV, adblockers etc. and also what backup applications/utilities
2. There are no profiles to save. No profiles exist on my computer.
   • That may be correct, but if Firefox has been used it will have created and used a profile, and that may still exist on your computer even if Firefox does not; at the moment; operate correctly. If any profile folder and profile files exist the information they contain may be important and worth trying to preserve.
3. I can't start Firefox in Safe Mode because I can't start Firefox at all.
   • I did suggest doing a clean reinstall, before attempting a restart. Sorry in my haste I failed to include a link on how to do that. Please see
     • Troubleshoot and diagnose Firefox problems_7-reinstall-firefox

Try to delete the profiles.ini file if there is such a file.

• http://kb.mozillazine.org/profiles.ini_file
• http://kb.mozillazine.org/Profile_folder_-_Firefox