No or not the custom leave warning when leaving while buffering

[peteruithoven]

While buffering (sending the doodle) we added a warning (onbeforeunload) so that when a user tries to close the page they get a warning. It's removed when it finished sending.

This works on desktop chome and safari. But on Firefox it doesn't show our custom warning. This is already filed as bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=588292
Mobile safari (iPad for example) and Opera ignore this completely.

There don't seem to be alternatives.

More info:
https://developer.mozilla.org/en-US/docs/Web/API/window.onbeforeunload?redirectlocale=en-US&redirectslug=DOM%2Fwindow.onbeforeunload