The first thing I'd recommend is to try running Firefox in Safe Mode to see if the issue goes away. It's possible that an add-on you have installed is slowing down the process.

According to your system details, you appear to have accessibility services running on Firefox. Sometimes these services can cause severe performance issues and crashes on Firefox. If possible, you should try disabling these services. See What is the Accessibility Service Indicator? for more information (in particular, the How do I disable Firefox Accessibility Service? section).

If all of the above fails to fix the problem, you may want to try performing a clean reinstall of Firefox. It's possible that a file was damaged or removed during the update process and this may be causing the issue. A clean reinstall is a good way to rule that out without losing the data you have in Firefox.

Hope one of these things helps.

I took the easiest and least threatening options first (because I have a slew of tabs open for pages that I watch) and was unsure if they would be remembered if I did a 'reinstall', but this morning I was reduced in options to doing the reinstall.

That not only solved the problem, but the tabs and previous session were remembered.

Wesley, I can't thank you enough! Great job!

Ray

No problem! Glad I could help.