The alerts on this page pop up immediately on WinNT with the 2000-04-16-15-M16 nightly binary. Given that, this looks like a DUP of bug 35248, "onClick fires on blur, not button up". See also bug 35884, "dialogue box (alert) extremely slow" -- based on what's reported there, you may see the alerts if you wait for a minute or more before doing anything else.
Sorry, there's a transposition in the last comment -- "onClick fires on blur, not button up" is bug 35284.
to Phil for testing on a Linux build...
*** This bug has been marked as a duplicate of 35284 ***