Today as I woke up my computer from sleep mode, Firefox was unresponsive and I had to use task manager to shut it down. The problem after restarting Firefox is that I have or had probably over four thousand tabs open in my previous session (yes I know it's a ridiculous amount), but Firefox didn't restore several hundred of the most recent tabs. I've had similar problems before but always managed to get all my tabs back from the sessionstore-backups -folder and JSONLZ4 -files located there. Currently the most recent upgrade.jsonlz4 -file shows the "Date modified" is 20.3. which is probably around the time I had problems the last time, which I resolved by moving such file to the main folder and renamed it sessionstore.js as per instructions, if I recall correctly. Using "Session History Scrounger for Firefox" makes it seem evident that the latest/biggest jsonlz4 -file is still in the same condition (around 3500 tabs), i.e. hasn't saved any pages after the recovery I made last month. For now I haven't tried to recover anything using the same method as above in case there's still a chance to restore the full session I had open until last night. So in essence my question is if the tabs opened between 20.3. and 8.4. are simply gone now? If that is the case I can live with it. But why hasn't or hadn't the jsonlz4 -file in sessionstore-backups saved any more pages after my last recovery from 20.3.? Or is there a file in some folder that I'm not aware of?