I am using Crunchbang, which is based on Debian stable. It is trivial to download and install either Firefox or Chrome from the internet, and they automatically

I am using Crunchbang, which is based on Debian stable. It is trivial to download and install either Firefox or Chrome from the internet, and they automatically update themselves (FF since v12; the betas have had auto-update for longer). For a more general solution you could look into apt-pinning, but there are some downsides depending on which way you go about it.