This is sort of a saga, but I'd rather give too much information than too little. I just got a new Windows 10 computer (Dell Inspiron 15 15000) and transferred all my stuff including firefox with all the tabs I had open. I usually have lots of tabs open, and I opened all the tabs on my new computer that I had had on the old one. For some reason I can't recall, I ended up with one window with one tab, and one window with all the tabs I'd had open on my old machine (including the one that was open by itself in the other window). I closed the window with the single tab, and continued using the window with many tabs. At the end of the day, I closed the window as usual and shut down the computer. The next day, I turned on my computer, opened up firefox, and no tabs! I checked to make sure that "open previous session at startup" was checked in the main settings, did some searching through the help files here, and found that the problem was that I hadn't gone in to the privacy settings to tell it to remember history. I fixed that, and did some more digging to figure out how to restore history, I don't remember how. I restarted Firefox, and it restored a previous session ... but not the one I wanted. It restored the window with the single tab that I'd only had open for about ten minutes, not the window with all my tabs (including that one) that I'd had open all day. Some more searching through the support here and I figured out how to restore the session I ACTUALLY wanted. I can't find the post now, but it told me to go to Help - Troubleshooting Information (I think--it LOOKED like the Troubleshooting Information page, from what I remember, although today it doesn't seem to have the option I used yesterday, so it might have been a different page) and see if there were two sessions, and if so, to click the other one, and see if that fixed things. It did! I got the window with all the tabs back, and closed the window with just the single tab, and went on with my day. Problem solved, right? No. I booted up my computer today, opened up Firefox, and what did I find? IT OPENED THE WINDOW WITH THE SINGLE TAB THAT I'D ONLY HAD OPEN BRIEFLY, INSTEAD OF THE WINDOW WITH ALL MY TABS IN IT THAT I'D HAD OPEN ALL DAY. First of all, I'd rather not have to deal with this again, so how can I make sure it doesn't? What is going on? Second, I can't find the help page that told me how to restore the correct window. This is a problem, because although all of the tabs I had open yesterday are in my history, when I go to the little library icon and look at "history" both the "recently closed windows" and "recently closed tabs" are empty. As far as Firefox is concerned, I haven't closed any windows or tabs since the last time the history was deleted, despite having lots of pages in the Recent History list that I sure don't have open right now. Clicking the three horizontal lines to get the main menu, there is no "restore previous session" as an option. I can go through the history and manually click on all the tabs that should be open, but that is REALLY a pain and I would like not to have to do this again. I have added the "Tab Session Manager" addon, so hopefully even if this is a recurring problem I can use that to get around it. (The addons listed below are all the addons I had when the problem occurred.) What the heck is going on here?