Beacon API based eager UI closing is broken on Firefox

[mstahv]

Description of the bug

It looks like the detach event is not firer "eagerly" when leaving the page (using a beacon request) when Firefox is used. With Safari I also noticed some issues with one project, but can't reproduce with a fresh project (some caching issue mayby on Safari 🤷‍♂️). With Chrome it always works.

Expected behavior

The detach event should be fired whan navigating away or closing the window within a reasonable time.

Minimal reproducible example

Override onDetach and see when it actually happens.

Versions

Flow: 24.3.9
Vaadin: 24.3.10
Java: Eclipse Adoptium 22.0.1
OS: aarch64 Mac OS X 14.4.1
Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:125.0) Gecko/20100101 Firefox/125.0

[mstahv]

Might be I was holding it wrong. FF at least sometimes don't properly do beacon request. https://bugzilla.mozilla.org/show_bug.cgi?id=1609653

[Legioth]

I wouldn't be surprised if this is just the way some browser implementations work and there's nothing we can do about it.

[TatuLund]

We have seen this Firefox problem also in our Vaadin 8 integration tests, as they are run both in Chrome and Firefox.

[TatuLund]

The workaround with Firefox is to do it in the old fashioned way with beforeUnload and XHR.