I use "restore previous session" religiously. Whenever i shut down, whether due to a problem or just normally, "restore previous session" is there and restores all my tabs. Sometimes after a crash, I get the "well, this is embarrassing" but when I click OK on that dialog to try anyway, it always restores. There have been a few times in the past when, for no apparent reason, "restore previous session" was greyed out when I restarted. My thankful workaround for this has been to open the library folder on my Mac, locate the Firefox folder in Application Support folder, select the "qqfh38jn.default" folder, go into Time Machine and replace that folder. Or sometimes I go INTO that folder and select "sessionstore.js" and This has always worked, and I breathe a sigh of relief when I restart Firefox and "restore previous session" is available and I can get all my tabs back (even if a few hours' worth of "opens and closes" are missing). Tonight I had to restart my computer because of a memory problem (got a system error that the OS was out of memory, which strangely happens once in a while). But I was able Firefox quit normally (i didnt have to force quit) and I restarted he computer. Safari started up normally and restored all of my tabs there, even though ironically Safari had hung and had to be force quit. I am researching a writing project and had six or seven Firefox windows open with 10-25 tabs each (yes, I do this all the time, for years now, and it isnt usually a problem, so no judgment please). I NEED THOSE TABS BACK DESPERATELY. Reconstructing them from history would be excruciating if it could even be done. (In the past, not everything seems to be in history in the order I want it; what I'd want is all of the tabs in the order they opened last time.) I've lost a lot of time on this already. I would be losing many many hours of work if I cant get those tabs back. if anyone can help re what happened, what is going on, and most of all how I can use Time Machine or a backup (or ANYTHING) to hopefully find the hidden file that saved/recorded my last session, I would be deeply appreciative. Going back a few hours or even days in Time Machine would help. Thanks so much! Samantha.