Have you tried Firefox's Troubleshoot Mode? Diagnose Firefox issues using Troubleshoot Mode

It should get Firefox started again. Please try it & let us know if you were successful. If not, I'll have to think of what else could be causing Firefox to be so broken. It could be one of the main installation files were damaged. If so, you might try reinstalling Firefox again to see if it can fix the corrupted or missing file. Reinstall from here: https://www.mozilla.org/en-US/firefox/new/

It is possible that some files in the profile folder got corrupted.

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

got your email, clicked on the highlighted in blue "diagnose....... and firefox opened, cleared the start up cache after a song and dance and now firefox works as it should...the song and dance, no matter what I clicked on a new tap would open with nothing there, somehow and don't remember how I got into trouble shoot and cleared the start up cache...I have it set to sanitize at close, why not make it to sanitize the start up cache as well at close, preventing this??? since 2000 all I have used is the Lizard on my Mac's, it's never been like this. I dream of better daze...thanks for your help......

You can find "Clear the startup cache..." on the "Help -> More Troubleshooting Information" (about:support) page. https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox