If you need to close Mozilla Firefox but don't want to lose all your open tabs, there are a couple of ways to save them. One little-known feature of Firefox is the ability to bookmark all open tabs into a separate folder, which allows you to easily re-open them later. However, some people do not want to clutter up their bookmarks with extra folders, in which case you can force a crash in Firefox that will automatically save your open tabs.
Save All Tabs
Click "Ctrl-Shift-D" to open "New Bookmarks."
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Enter a descriptive name in the "Name" folder, which has the date you saved the tabs.
Click "Add Bookmarks" to save all your open tabs. To reopen them, right-click the folder in your bookmarks list and select "Open All in Tabs."
Right-click an empty area of the Windows Taskbar and select "Start Task Manager."
Click the "Processes" tab.
Right-click "firefox.exe" in the processes list and select "End Process." Click "End Process" in the confirmation window to close Firefox.
Run Firefox again and you will see a recovery console pop-up. Choose "Restore previous session" and all your previous tabs will re-open.