Did as you said, ran delayed backup, froze at about 2.1% with the following in the log:
NS_ERROR_FAILURE: Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIFile.initWithPath] febe.js:1955
Cleared all again, ran all the way through with a few warnings about not being able to find an addon, which I just OKd. Hoping that I have a good backup now - going to wipe out current installation and try to get back up again! Something is just really messed up in my current FF. Popup windows are empty, nothing prints right, I have to regularly "restore previous session" and other nasty things. Hopefully I'll be able to rebuild FF to a working version of the features I have and love now. If worst case happens, I have shadow copies of the whole drive I can restore from!