I don't know about cursing any engineers, but I'm running a 3.something version for Firefox because I have a set of plug-ins that work, and have failed to work in later versions, and I get to do what I want in a way that I'm happy with.

If there's some overwhelming reason it would be in my own best interest to stop using 3.x I'm certainly interested to hear about it.

The number of sites that appear to take advantage of more current FF features is, for me, minuscule, and I can visit the site in Chrome or something if needed.