alert() in our browsers

Implementation of alert() in Firefox 3 and 4 allows you to block client with modal alert dialog as simple as:

for (var i = 0; i < 1000; i++) {
        alert('Alert #' + i + ' of 1000')
}

try yourself

Chromium allows you prevent some page from creating such annoying dialogs. Opera suggests You to switch js off on this page. Only FF shows modal alert dialog (you cannot even close your browser btw).

UPD: Trunk Builds: Fixed: 61098 - Allow aborting modal alert() loops in javascript The bug was reported almost 10 years ago.