Merge pull request
#3510 from minrk/ffisbroken
use `window.onbeforeunload=` for nav-away warning
Firefox 22 broke `$(window).on("beforeunload")` somehow, for some reason, resulting in always showing a dialog, regardless of the function's return value.
closes
#3509
The only fix I could find was resorting to the basic low-level API.
