I'm having a similar problem to other posts I've seen here at support.mozilla.org, but not exactly the same, and none of the solutions are working for me. I was using my Firefox ("FF") for Mac v77.0.1 with many tabs across 3 windows (as I've done for years). I Quit FF, shutdown Mac, and when I restarted Mac and FF, the windows and tabs did not reopen (as opposed to always reopening just fine, for years and years). I looked under the History menu, and the missing windows and tabs did NOT list in the Recently Closed Tabs or Recently Closed Windows, BUT it DID list tabs and windows that I HAD recently closed. I went ahead and selected Restore All Tabs and Restore All Windows, hoping that maybe it'd somehow open my last opened windows/tabs, but not only did that not happen, but it didn't even open the actually recently closed tabs/windows it had listed. Then, the History drop down menu just greyed out the Recently Closed Tabs and Recently Closed Windows options under History. '''''NOTE: It might be best to next skip down to MY Reply to this post (solution??), and then up to my Update/Edit (down below), before continuing right here to read my efforts to solve this!''''' Luckily, I had just backed up my Mac right before shutdown, so I grabbed the sessionstore.jsonlz4 file from most recent backup, Scrounged it at https://www.jeffersonscher.com/ffu/scrounger.html, which produced an HTML that lists all the windows/tabs that I had open (including the Back-Forward History) before Quitting FF & Shutting Down Mac. Then I followed these instructions I've seen many places: 1. quit FF 2. rename sessionstore.jsonlzr in my FF Profile to sessionstoreOLD.jsonlzr 3. copy sessionstore.jsonlzr (and next recovery.jsonlz, and next previous.jsonlzr) from my Mac backup 4. paste sessionstore.jsonlzr into the FF Profile on Mac (or paste recovery.jsonlzr or previous.jsonlzr, renaming them sessionstore.jsonlzr once pasted there) 5. open FF Once I did those steps 1-5, it did NOT open any of my windows/tabs from previous session. I even tried renaming my whole FF Profile from 2d7si5hi.default to 2d7si5hiOLD.default, and then copying the FF profile backup and pasting into Mac next to the old FF Profile. Once reopening FF, still no previous windows/tabs. I even tried Trashing FF Profile 2d7si5hiOLD.default, before pasting in FF Profile from backup. Once reopening FF, still no previous windows/tabs. I then did all the above with even older backups (from about 2 weeks ago). In THIS case, ONLY ONE of the 3 windows opens with lots of tabs (but not the other 2 windows of tabs). I then updated my FF to v78.7.0esr, and went through ALLLLLL the above steps again, and the results were the same (unsuccessful). I then tried creating a new FF profile, copying ALL contents from most recent FF profile backup and pasting into the new FF profile (per jscher2000's instructions - but without having done the Refresh FF - at https://support.mozilla.org/en-US/questions/1136981) .... again, none of the previous windows/tabs showed up. '''SO - anyone know how to get my FF to show all the windows/tabs that ARE present in my sessionstore.jsonlzr backups? Am I missing some step(s)??''' By the way, in both FF v77.0.1 and v78.7.0esr, this glitchiness is also happening: * FF Preferences won't open * Help > Troubleshooting Information won't open (except for SOMEtimes if I already have a new Window open) Thanks much!! '''UPDATE/EDIT!''': ''Whoa. Weird''. I just happened to accidentally toggle to my Mac Dashboard (which I rarely use), and underplayed beneath the Dashboard Widgets were THE THREE MISSING FF WINDOWS OF TABS - which I could toggle between there at the Dashboard. I toggled back from Dashboard to Desktop, closed the FF that was open and NOT showing the windows/tabs, then toggled back to Dashboard, and the FF windows/tabs were no longer there. THEN, I reopened FF, again no windows/tabs, but then a toggle back to Dashboard - and boom, there they are! '''Say what??''' OKAY - so FF ''is'' accessing/seeing the windows/tabs, just not displaying them within FF, but, instead, as standalone items ''behind'' Widgets on the Dashboard. Does this give anybody any insight on what's going on and how to fix it (way above my head!)?