Well, that was a stressful and thoroughly wasted hour of my life!
I have deliberately not allowed Firefux to update for a while (because of certain add-ons). Well, it's been fucking up more and more lately, and has been a MASSIVE memory hog (at one point I looked and it was taking up 3 GB of memory!)
So I let it update, to see if I could get some speed improvements and fewer freezes.
And the stupid designers STILL have the damn tabs at the top, ABOVE the main menu, and the links menu! It took me (particularly since I'm WAY past my limits currently) possibly half an hour of stressful time finding and implementing the 'fix' for that... a fix for something that should not be an issue to start with!
After doing that, and starting to get my 'start page links' settled, I happened to check the Search box. And I'd lost THE main thing that keeps me tied to Firefox in the first place, but which I'd actually forgotten: an add-on that creates a pull-down menu giving direct access to ALL of the website Search boxes from as many websites as one desires. Because of how I use the internet, I have THIRTY website Search boxes there (and, yes, I use each of them)! [e.g. I have two just for this Forum: a 'words in post search' and a 'words in Subject search'.] The difference in time, effort, and hassle, of having to go to each of those websites, going to any dedicated Search page for the complex searches, and THEN getting results - for every instance of a search for something from them, vs. having all that available immediately from the Search box in the corner? No fucking way I'm giving that up for ANY supposed performance gain!
So I moved every bit of Firefox (new) out of the 'Programs' and 'Users' areas, and copied my Firefox backup (from day before yesterday, so I lost a bit of stuff) into the folders.
Still... I guess there is one thing I got out of this: there will NEVER be a time where I consider updating it again until it completely ceases working. At which time I may move to Opera, or Chrome.