While typing a long function in a cell, I somehow got my copy of Firefox here to interpret the backspace key as page navigation before my typing had been committed. The browser navigated back in history, leaving the page. When I went forward again to return to my notebook, my typing was lost.
This reminded me that I need to disable the moronic default backspace behavior in my Firefox here, but there is also an Observable bug here (which I have run into a couple of other times for other reasons, but can’t really remember the details) causing data loss.
If there is something typed in a cell but the cell has not yet been run / saved, the notebook page should put up a modal prompt before letting the browser navigate away. This won’t show up too often (because most of the time the content of all of the cells is committed) so it shouldn’t ever bother anyone. But could save someone from disaster if they for whatever reason do a ton of typing without committing partial results along the way.