It is because you deleted the Profile that the Developer was using as Compatible Mode. Suggest backup your bookmarks :

• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Uninstall both and then reinstall after deleting all folders of Mozilla.

So because it was hooked together I do not know what files would stop that.

Uninstall and reinstall? That's an absurd request when all this app needs to do is use the correct profile which is designated as default. Now I need to lose all of my persisted session information, saved logins, history, etc, or waste even more time attempting to back it up and restore it (which at this point I'm also certain will fail) to fix this easily solvable issue for the developers? Unbelievable and unacceptable. This has now motivated me to make the full time switch over to Chrome. Atrocious.

Well , absurd or not it will work. Stick around for some other help. Excuse me. Volunteers spending or spare time helping do not need that.

It's not a reasonable instruction to give someone. If the developer profile is removed, it is immediately replaced by another developer profile, which becomes the default profile. Why is FF incapable of using that as the compatible profile and going about it's business accordingly? This is a bug in the application itself that needs correction. There is no reason that an end user should have to lose everything because of a developer mistake.

Since the Profile can be backed up and it is in a different location then the program files it can be uninstalled. This is a common fix and works especially when it is years worth of updates.

I suggested it and did not put the 1/2 page support article in to my reply as I did not think it was needed to legitimize my suggestion.

Hang in someone else will come along with something you may like better.