"User prompts that are spawned from beforeunload event handlers, are dismissed implicitly upon navigation or close window, regardless of the defined user prompt handler."
I think this is causing timeouts in tests:
This turned out to be a bug in MiniBrowser, it has nothing to do with WebDriver, nor with beforeunload. The problem is that the affected tests use a popup window, with an entry that is filled with send keys command. The send keys command is failing because in the new window the focus is not in the web view, it's in the toolbar, so key events are sent to the toolbar instead.
Created attachment 347069 [details]
Committed r234915: <https://trac.webkit.org/changeset/234915>