Could you check whether either of these are available (not hidden or grayed out): * "3-bar" menu button > History > Restore Previous Session * (menu bar) History > Restore Previous Session If they are missing or grayed, check either: * "3-bar" menu button > History > Recently Closed Windows * "Library" toolbar button > History > Recently Closed Windows * (menu bar) History > Recently Closed Windows Are you able to find windows closed during your previous session there? ---- One issue a few different users have reported is a hidden or off-screen window that prevents Firefox from actually shutting down when you close the last window. So when you hit the icon again, it just adds a new window, like Ctrl+N. To check for unexpected windows, try 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 In the left column, click Open Tabs. This should display all your active windows and their tabs.