PageGroupLoadDeferrer calls suspendActiveDOMObjects() on all platforms but Mac, which results in e.g. DOM timers working in a page beneath a modal dialog. This doesn't match Safari for Windows or Firefox, and generally doesn't make much sense.
Created attachment 39799 [details]
Committed revision 48540.
Note that Firefox doesn't fully pass the test - even though timers are disabled while the modal alert and dialog are displayed, they still run while he latter is being created.