But it would involve source-diving. Spidermonkey is the Mozilla JavaScript library (written in C). If you were feeling brave, you could track down the setTimeout() function and make it a "do nothing" function, then rebuild Firefox.

Personally, I leave that sort of thing well alone - I'll only have anything to do with mods using XUL/JavaScript. Preferably when someone else has written the extension ;-)

If you're not a programmer or are but don't fancy hacking this, I'd suggest that you consider using the NoScript extension, which allows you to run JavaScript only for trusted sites. Not exactly what you are asking for, but a possible solution.