Hi Doug, it's been many hours, so maybe you already tried the following, but just in case: 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 ---- If that doesn't help... One issue some users have encountered recently is a non-visible window that keeps running when they click "X" to close the last visible window. Since there is a window running, Firefox doesn't close, and when you use the shortcut, Firefox creates a new window in the existing session rather than restoring the close window. To check for non-visible windows, you can try Firefox View. 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 open it Click "Open Tabs" to show all of the open windows with their respective tabs. If there is an unexpected window here, that could be causing the problem. Note: you also can avoid the problem by quitting Firefox through the menu. Either: * menu button > Exit * (menu bar or Alt+F) File > Exit