I'm stuck on Debian oldstable (lenny) for the moment. I needed to upgrade to Firefox 3.5 which is available in lenny-backports. After a bit of searching and fiddling, it turned-out to be very easy. There is basically just one thing you have to do---add the following lines to /etc/apt/sources.list:
deb http://backports.debian.org/debian-backports lenny-backports main contrib non-freeOf course, you'll need to change lenny to the stable verison you're using if you're not on lenny. After that update, do the usual apt-get magic:
apt-get update apt-get install the-package-you-want-to-upgradeAssuming it is in backports, it should "just work".
Note that the standard instructions tell you to add preferences so that only the package you want to upgrade is allowed from backports. But, if that package depends on later versions of anything, you'll need to add preferences for those packages, and if those packages depend on later versions, you'll need to add more preferences, etc. Seriously? I think the author is just being too darned careful. :-) Maybe it's better to comment-out that sources.list backports line after you've installed what you wanted...