Post

The CloseWatcher API landed in Firefox 149, making it easy to listen for platform-specific 'dismiss' signals. Here's how it works:

Is there any way to polyfill this?

I think mostly yes, the anti-abuse mechanics would be difficult (impossible?) but then also not really important because a polyfill couldn't handle the Android back gesture.

Yeah I'm mostly interested in just that - polyfilling the browser / gesture back action.

Yeah that's essentially not possible. You *might* be able to do something very hacky with the navigation API and intercepting back navigations but I'm not sure how much that's exposed.