If I had a dollar for every time I'd accidentally closed a browser tab -- or worse, an entire windowful of 'em -- I'd be rich.
But there's a simple keyboard shortcut that can instantly correct this error: Ctrl-Shift-T.
Or Apple-Shift-T, if you're using a Mac.
Honestly, I'm a little embarrassed to admit I only discovered the shortcut a few months back, but it's changed my life ever since. (I used to use a browser extension called TooManyTabs to do something similar, but this is way better.)
Just know that some browsers work better than others. With Chrome or Safari, you can restore an entire window full of tabs with this one quick three-button press, so long as your browser is open.
But with Firefox or Microsoft Edge, you can only restore tabs one at a time, and only if you opened those exact tabs in the same browser window.
If this keyboard shortcut is new to me, I'm betting it could be new to you too. If not, maybe it'll help someone else?