As of Firefox version 94, you will no longer receive a warning when you try to close a Firefox window with multiple open tabs. Fortunately, the feature is not completely removed and you can enable it from the Firefox settings menu.
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Get a warning when you close multiple tabs in Firefox
To re-enable the missing prompt in Firefox, first open Firefox on your Windows, Mac, Linux, or Chromebook computer.
In Firefox, click on the three horizontal bars in the upper right corner.
Select “Settings” in the menu that opens.
Click “General” in the “Settings” window in the left sidebar.
On the “General” screen in the “Tabs” section, enable the “Confirm before closing multiple tabs” option.
Tip: To re-disable the prompt that appears when you close multiple tabs, disable the “Confirm Before Closing Multiple Tabs” option.
And that’s all it takes. Going forward, when you close a window with multiple open tabs in it, Firefox will display a warning before the window actually closes.
Did you know that you can selectively close multiple tabs at once in both Firefox and Chrome?
RELATED: How to select and close multiple Chrome or Firefox tabs at once