IMac hard drive failed. An authorized apple reseller installed a new hard drive and one memory stick and restored all my existing files, including Firefox history, from my external backup drive. The installer also upgraded my os x from 10.11.6 to 10.12.6 and Firefox (possibly an auto-update) to 60.0.2. Firefox began crashing as much as every minute. "Gaa..window" could restore my browsing history windows and tabs with no problem--even when I would crash all the way down to login or even restart. This was an impossible situation and I did restore using a dozen crash reports to Firefox, which should be documented. But then the worst happened; I think that during one of these crashes, Firefox auto-updated itself from 60.0.2 to 61.0. Whether that caused the history loss, I cannot say. However at about that moment in the midst of one of these crashes, history windows and tabs stopped restoring. Selecting the history menu button showed two or three very recent history items. I tried "Show all history" and the items were paltry and recent. I tried the (now) oldest option from the library menu, which is now "June" and found a couple of weeks worth of random individual tabs some of which may have predated the failure of the hard drive originally, but none of the lost windows and tabs that I had open minutes earlier. I can speculate that what happened has something to do with the Firefox auto-updating to the higher version that happened during one of these crashes, also minutes ago, and I have perhaps some random fragment of the two versions--who knows. I thought I could do a restore using my external back up drive and Time Machine with Apple support of the phone line to no avail. I have a desktop folder called "Old Firefox Data" that has bookmark data but no browser history items visible, and will not restore anyway. If it helps with the original call to Apple on the subject continuous crashes, the technician said he had OS x 10.12.6 and Firefox 60.0.2 both running and had no crashes. Whether he had many window and tabs open, I cannot say. I was also advised by Apple to uninstall and then reinstall Firefox, which I did. Perhaps I should tell you that my suddenly missing history on Firefox came from Google searches. Also the lost browsing history was a dozen or so research articles, thus the loss is pretty hefty and probably not replaceable if I can't restore it. Time Machine has not proved to be much help, however I can still try to see if I can access the lost history directly through my external backup drive. Also I have spent most of a day looking at Mozilla help article and found them to arcane, not to the point, and perhaps outdated. Thanks,