Firefox updated to 155.0.1 - now no Rt-Clk, no rearranging of tabs, and menu buttons across top of windows all inert. Win10 desktop. HELP!

Can you start into troubleshoot mode by holding Shift key when launching Firefox?

Yes, it starts in troubleshooting mode, but the 3 problems described still persist. As a result, I'm slowly switching to google chrome, but my productivity is way down - by 50% or more.

The fact most of the interactive elements are inactive or unable to receive focus is surprising.

I'd normally advise to create a new profile on the side to test with clean slate (if you can't use the built–in functions, you can also Win + R and launch: firefox.exe -P from there to get the profile selector a create a blank testing one there and open that one) — to see if "fresh start" works better, or it's something system–wide on your environment:(

Well I tried the Win-R and firefox.exe -p. Created a test-blank profile. Opened a half-dozen pages. Found that all 3 problems were absent. Very promising progress! Is there a way to copy all my Open Windows, Tabs, and AddIns over to a new profile?

btw . . . I normally have 15 Windows open, with between 12 and 350 carefully sorted categorized and organized subjects/tabs each. I'd really hate having to recreate it all manually.

You can basically start copying files from your old profile to the new one one data class at a step to identify which one might be causing the issue. See this article on what files to copy.