The page changes from customize to the Firefox Home / new tab page, or it just closes?

The customize panel can be immediately dismissed with the Esc key. Not that there is any reason for you or the nearest cat to be pressing the Esc key, but that was the first thing that came to mind. In case Firefox is confused about that key being pressed, try pressing it rapidly several times in a row before customizing again.

It's not the escape key. I just rolled back to 114.0 .2 and the problem has disappeared (unfortunately I lost all saved logins and other data but at least backed up bookmarks). I'll try going back to 115.0.3 next and ifj that works then I'll try 115.10 which is where I ran into the problem.

Did Firefox tell you it needed to create a new profile? Your old profile is still on disk and after things setting down you can try migrating files (not sure which files might be associated with the problem, so you'll probably want to do it a little at a time). See:

• Recovering important data from an old profile
• The about:profiles page will have buttons to open the Root Directory of your current and your various historical profiles

You can try "Clear the startup cache..." via the "Help -> More Troubleshooting Information" (about:support).

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox

Ok..here's the latest and it befuddles me. As I mentioned I went back to 114.0.2 and the problem disappeared. The home page button was already to the left side of the address box so I didn't have to change anything. I redid my settings (home page, cookies...etc) then updated to 115.0.3 and since everything LOOKED ok, I updated to 115.10.0esr. The Home page button was in the correct spot, but when I went to customize the tool bar (just to see if I could), the problem was there again: I could not get the customize toolbar page to come up. It would flash momentarily then the page would automatically close and I was at a new browser page. Tried to bring up the customize toolbar page repeatedly and problem occurred every time. Pressed the escape key at various times to no avail. I wondered if the problem also occurred on the version 115.0.3 since I didn't test it on that page. That is, I didn't test to see if the customize toolbar page would come up on that version...since everything seemed to be where I wanted it I just automatically updated to 115.10.0esr. So I restarted at 114.0.2 and updated in the same order as before except this time I checked at every version to see if the customize toobar screen would come up. As before I updated my settings on the 114.0.2 (homepage, cookies, download location etc) along with the ublock origin and 1 other extension as I have always done. At 115.0.3esr everything worked along with the customize toobar page. And this time, when I returned to the scene of the crime 115.10.0esr EVERYTHING worked, including the customize toolbar page! Whyi? I don't know why this all occurred but if it happens again when a new version installs, I'll decide whether it's worth the trouble or just decide to switch to another browser. Thanks for the help you tried to provide. I do appreciate your time but I don't appreciate having to go to these lengths just to keep things the same from version to version.

By the way, here's the kicker. After I had it all solved I did as you suggested in your second post about setting up sync. When I went to set up sync, I was immediately taken to a page that said Thanks for installing Adblock and Adblock plus. So I tried to customize toolbar and problem reappeared! I didn't even ask for Adblock or Adblock plus to be installed. I uninstalled the two culprits and tried again and the problem was solved. I have not installed Adblock nor adblock plus in years so I'm wondering if they somehow got installed automatically when i visited a web page I shouldn't have. Or, were they part of a Sync file I had set up at one time? Still doesn't explain how they could have been installed several days ago when I got updated to 115.10.0esr since I haven't used sync in ages. Anyway, if anyone has the problem with not being able to bring up their customize toolbar page, make sure adblock and adblock plus are not installed.