pop-ups make safari unusable, force user to "force quit" safari.
JavaScript alert dialogs have nothing to do with pop-up blocking as they are not pop-up windows in that sense. The manner in which alert dialogs are displayed is application-specific so this may be more of a Safari issue than a WebKit issue.
<rdar://problem/5767363>
*** Bug 17859 has been marked as a duplicate of this bug. ***