Many thanks, @burnout426. I followed your instructions, but clearly I had made a mistake by closing Opera early on after I noticed the mistake, and while I had a Tabs_ file from the day before the crash, I only had a Session_ file from afterward, so those previous windows and tabs are gone. Thanks for the tip on backing up. I'm moving to a new computer, and will need to reestablish as many of those windows and tabs from History as I can or wish to, and then copy or sync the necessary files to reproduce that on the new system.