Firefox's Most Helpful Hotkey

Countless times I happened to close the tab by mistake, which I had to leave open. At best, it was annoying, at worst, it turned out to be a catastrophe. But I have no more such problems. Why, you ask? Because now I know the most useful hotkey in Firefox ... Command-Shift-T.
The next time you close the desired tab, just press Command-Shift-T, and the tab will magically return! Now that you know about Command-Shift-T, try to imagine your life without it.
Translator's note. Command-Shift-T - for OS X, Ctrl-Shift-T - under Windows.