Sorry to hear about this problem. If this just happened, could you check whether they are in a closed window? Either: * "3-bar" menu button > History > Recently Closed Windows * (menu bar or Alt+S) History > Recently Closed Windows * Ctrl+Shift+N If you find what you're looking for there, the problem might be that Firefox didn't shut down properly when you closed that window. For example, there might have been a non-visible window (off screen or on a second desktop) that kept Firefox running. To work around this: (A) Quit Firefox using the menu. Either: * "3-bar" menu button > Exit * (menu bar or Alt+F) File > Exit (B) Check Firefox View for additional windows. You can call it up using either: * click the file drawer icon at the left end of the tabs bar * type or paste '''about:firefoxview''' in the address bar and press Enter to load it Then in the left column, click Open Tabs to show a diagram of all the open windows. Anything unexpected here? (C) Check for additional desktops Hold down the Windows key, then tap and release the Tab key, and release the Windows key. After a short delay, Windows should display thumbnails of open windows and a desktop switcher at the bottom. Hopefully this will reduce the incidence of lost tabs caused by closed windows. '''''If you are losing some tabs out of windows that are restored, so the restore within that window is partial, that sounds like a different issue.'''''