greasemonkey - Javascript page load delay of specific set of pages -

i want delay specific set of webpages using small greasemonkey script. basically, if website being loaded part of set of pages, want delay time page takes load. e.g. if page being loaded "http://www.a.com/","http://www.a.com/b", etc. want delay load 30 secs.

assuming dushara's comment correct:

"see xkcd.com/862 poster wants. (hover mouse on image see reasoning). in fact, found question while googling same thing."

then not possible in greasemonkey. reason gm fires after page has loaded (except slow pictures or ajax calls). user see page , would, say, flash blank 30 seconds... but, after quick eyeballs have seen much. ;)

update: possible in greasemonkey (with @run-at document-start directive -- added august 2011). see this answer example.

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note xkcd's creator uses good, old-fashioned willpower implement "simple 30-second delay". his blog entry:

"lots of people have asked me system used implement restriction in alt-text of today’s comic.
...
made rule finished task, or got bored it, had power off computer."

see also: "browser extension (or other software) delay page load" -- has links proper extensions people created this.