%APPDATA%\Mozilla\Firefox\Profiles

Hi Rob, if your Firefox doesn't restore your previous session automatically, could you check whether either of these are available (not hidden or grayed out): * "3-bar" menu button > Restore Previous Session * (menu bar) History > Restore Previous Session If Firefox does restore your session automatically, or those items are missing or grayed, check either: * "3-bar" menu button > Library > History > Recently Closed Windows * "Library" toolbar button > History > Recently Closed Windows * (menu bar) History > Recently Closed Windows By default, a restored session will have up to 3 closed windows to restore. Anything? ---- If that doesn't help... Firefox creates numerous session history files, but because session history is only for the immediately previous session, it is unfortunately too easy to lose it. Could you start by making a backup of your existing session history files? Here's how: ''Do not exit Firefox, or if you closed it, don't re-open it.'' '''(1) To open your profile folder...''' ''If Firefox is still running:'' You can open your current Firefox settings (AKA Firefox profile) folder using either * "3-bar" menu button > "?" Help > Troubleshooting Information * (menu bar) Help > Troubleshooting Information * type or paste '''about:support''' in the address bar and press Enter In the first table on the page, in the Profile Folder row, click the "Open Folder" button. ''If Firefox is closed:'' Type or paste the following into the Windows Run dialog or the system search box and press Enter to launch Windows Explorer: %APPDATA%\Mozilla\Firefox\Profiles In that folder, do you see a semi-randomly-named folder? If so, click into it. If you find multiple such folders, find the one that was most recently updated. '''(2) Copy out session history files''' In your profile folder, double-click into the '''sessionstore-backups''' folder. Save all files here to a safe location such as your Documents folder. '''(3) What files did you find?''' The kinds of files you may find among your sessionstore files are: * recovery.jsonlz4: the windows and tabs in your currently live Firefox session (or, if Firefox crashed at the last shutdown and is still closed, your last session) * recovery.baklz4: a backup copy of recovery.jsonlz4 * previous.jsonlz4: the windows and tabs in your last Firefox session * upgrade.jsonlz4-''build_id'': the windows and tabs in the Firefox session that was live at the time of your last update Could you take a look at what you have and the date/time of the various files to see whether you think any of them would have the missing tabs? To preview the contents of a file, you can drag and drop it onto a tool on my site, then click Scrounge URLs: https://www.jeffersonscher.com/ffu/scrounger.html ''If you don't get a list within 15 seconds, that probably means the script is caught in a loop. You may need to close the tab to avoid a tab crash and then try again in a new tab.'' If you get a useful list, use the Save List button to archive it as a web page of clickable links for future reference, in case no other approach is successful.