The short answer to fixing the issue is to create a new Firefox profile - after hours of frustration, that was the best but least preferable solution I could find.
If you are unfamiliar with the process of creating a profile, follow these instructions:
https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profilesFirst, I left my existing default profile there and renamed it so that I could get back to it as needed. I also backed-up my bookmarks, and made a note of all of the add-ons and extensions I had previously installed in FF.
I then created a new Profile - note that any new profile will not have your add-ons and extensions installed (yes, bummer). But it also gives you a chance to clean out some of those unused, or outdated add-ons and extensions you had not yet bothered to remove.
You have the option of starting FF with a designated profile, or to be prompted each time you start FF. In the short term, until you get all of your stuff reinstalled, like Firebug, its nice to go back to the old profile.
Restore your bookmarks too, and you should be good to go. I've got a few less hairs, but being bald, no one has noticed.
Hope this helps the next guy who gets caught by this nasty feature.