Never mind. After registering to post my question (using Edge), the process eventually led to a step that opened Firefox, but this time it came up also with a tab that said it was having a problem restoring my old tabs. That solved the problem, because I could deselect the hostile tab, and everything is fine again.

So the process of posting my question solved the problem inadvertently.

Hi rwhadsell, Firefox will always attempt an automatic session recovery after a crash, and show the list screen if that fails for some reason. To have Firefox skip the automatic recovery and go straight to the list screen:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Double-click the browser.sessionstore.max_resumed_crashes preference and change the value from 1 to 0 (that's a zero) and click OK.

A way out of the trap is to (force it if needed) Close Firefox. Wait about 20 seconds for Firefox to finish closing. Right-click on the Firefox icon and select Open New Window. +++++++++++++++++++++++++++++++++ Sometimes this works. If it opens, close it by Menu > File > Exit. This will flush out that web page from the Session Store.