Does the (IMO rather overzealous) autosave not work for you?

Web browsers often handle this or can get configured to handle it.

Ok, I'll check out how to configure my browser.

We don't need more nannyware.

This isn't "configure the web browser". Probably could be done strictly in the browser by an extension which would be supremely annoying. Normally it is done by a drop of Javascript as part of the page. Trivial to add. Useful to the 50% of users who it helps. Annoying to the 50% of users who can't stand it. I am more often in the "can't stand it" side, though not always.

This is one of the things we intended auto-save to mitigate, so if that's not working we'll want to look into that.

@manassehkatz Perhaps this could be a setting

@manassehkatz‭ Firefox (for example) by default whines like crazy each time you want to close a window. I have to enable non-default settings to make that behavior go away. No need for extensions or plug-ins, just run it as it comes by default.

@Lundin I find Firefox complains about closing a window with multiple tabs, but it does not (at least for me) complain about closing individual tabs, unless an application tells it do so.