Just stumbled upon this link to the Firefox 1.0 PR Release Notes (PR1 is not released yet), and noticed something that will relieve a LOT of headaches.
Undetectable document.all support for site compatibility and improved compatibility for keyboard accelerators further smooth the transition for IE users
This means there's no need to re-code a lot of your javascript to stay compatable with Firefox. Of course it's still good if you do it the 'correct' way, with the standard document.getElementById(), but this should alleviate a lot of corporate intranet headaches, where some complex sites rely on Microsoft's proprietary javascript extensions.