Just stumbled across this today, and figured it's worth sharing. Firefox maintains a version called Extended Support Release (ESR). It's similar to other projects also releasing a Long Term Support variant of their frequently updated product.

The benefit here is that bugfixes and security issues are addressed, but new features roll in on a less frequent basis. Doug, this may be of interest to you, as I know you wanted to hold onto Firefox 3 for a while.

I'm switching some automated tests over to ESR, to minimize the changes of a new version breaking the automated tests due to a new bug. People who maintain kiosk systems, or do mass deploys may also be interested.