- Just open the bookmarks library (<Ctrl> + <Shift> + <O>);
- press <Ctrl> + <Z> once;
- you can now check if your favorite bookmark is back (just check the "Bookmarks" menu, or by checking "All Bookmarks" → "Bookmarks Menu", or by using the "Search Bookmarks" feature).
- <Ctrl> + <Shift> + <Z> performs a generic "undo" function; therefore, it can undo not only bookmark deletion, but also bookmark addition or edit operation;
- if you press this key combination several times, it will undo several last bookmark changes (though I'm not sure what's the depth of this "undo queue");
- don't worry either if you've undone some useful bookmark changes: there's also a generic "redo" key combination: <Ctrl> + <Shift> + <Z> (or <Shift> + <Ctrl> + <Z>, if you prefer).