I have now tried the fix I described in thread #8 on a second computer that had the identical issue with Firefox, this time saving the bookmarks and passwords files as shown. This second computer is also now working fine.
For what its worth, if you do not know how to import the bookmark.json file, open Firefox, select Bookmarks, Organize Bookmarks, then choose Import and browse to the location where you saved the file.
To get your passwords back, simply copy the 2 password files into the Application Data\Mozilla\Firefox\Profiles\xxxxxxxx.default folder (with Firefox closed).
I hope this bit of troubleshooting will help others here. ~~ snip ~~
Good luck to all!