10.0.5esr is better
You'd do better to ditch 3.6 and switch to the long-term-support Firefox based on 10. (Currently at 10.0.5) http://www.mozilla.org/en-US/firefox/organizations/all.html
I'm quite happily using the latest 13.0.1 but it's well worth knowing that there is an official version that's getting only bugfixes, if you're supporting an organisation or allergic to new features being dropped on you. (I am allergic that way, but so far Firefox hasn't done anything bad enough to annoy me back to 10).