Here are some things to check: Did Firefox fail to restore your session? Check whether either of these are available (not hidden or grayed out): * "3-bar" menu button > History > Restore Previous Session * (menu bar or Alt+S) History > Restore Previous Session If you used either of those, or they are missing or grayed, check for closed windows using either: * "3-bar" menu button > History > Recently Closed Windows * (menu bar or Alt+S) History > Recently Closed Windows Were your missing tabs in any of the closed windows? If not, check for non-visible open windows using Firefox View. Either: * click the "file drawer" button at the left end of the tab bar * type or paste '''about:firefoxview''' in the address bar and press Enter to load it Click "Open Tabs" in the left column, and Firefox should display boxes representing all the open windows. Anything listed here that you do not see on screen? Those might be off screen due to unhelpful coordinates, or they might be on a different desktop. Are you able to find anything so far? The last possibility is that there are closed tabs in ''one'' of your windows that you can restore using the menu. Either: * "3-bar" menu button > History > Recently Closed Tabs * (menu bar or Alt+S) History > Recently Closed Tabs Beyond that, we have to dip into history or mine some files on disk.