### <kbd>Ctrl</kbd> + <kbd>Shift</kbd> + <kbd>Z</kbd> is undo instead of redo...unless there are no more items to undo

I would expect this to behave identically to <kbd>Ctrl</kbd> + <kbd>Y</kbd> (redo), as it does everywhere else (Firefox 104.0a1 on Windows 10).  At any rate, it certainly should not _sometimes_ undo and _sometimes_ redo.

[![A screen recording of "Testing" "One" "Two" being typed each on one line.  Then "One" and "Two" vanish, and "Testing" begins flashing](https://i.sstatic.net/DNNLP.gif)](https://i.sstatic.net/DNNLP.gif)