My Debian Squeeze system uses the Debian Mozilla APT Archive to bring newer versions of Iceweasel (aka Firefox) and Icedove (aka Thunderbird) than are available in the stock releases.
An update today brought Iceweasel/Firefox 10.0 into my Debian Squeeze laptop. The Firefox release pace has been extremely fast lately, and it's nice to get the latest releases packaged up for Debian.
That said, I'd love to see a newer version of Icedove/Thunderbird. The Debian Mozilla APT Archive version is stuck at 5.0, and even Debian Backports and Wheezy are mired in the 3.6.x era.
Disclaimer: I know, I KNOW I can go to Mozilla, install from there and have the Mozilla repository keep my Firefox and Thunderbird up to date. I know. I haven't done it. I guess I'm more comfortable with the packages made by and for Debian. No good reason, as I use Google packages for Chrome.