This allows the user to enable the April Fools mode, if they want.
@run-at document-start, so TM & VM users don't need to wait for the
page to load for the auto-refresh.
Change to using vanilla JavaScript, as Greasemonkey 4 doesn't obey
any @run-at settings and will have this run anywhere from
document-start (i.e. prior to jQuery loading) to document-end.