have a look at the output:
# apt-cache policy iceweasel
iceweasel:
Installiert: (keine)
Installationskandidat: 38.1.1esr-1
Versionstabelle:
39.0.3-1 0
1 http://ftp.de.debian.org/debian/ experimental/main amd64 Packages
38.1.1esr-1 0
500 http://ftp.de.debian.org/debian/ unstable/main amd64 Packages
38.1.0esr-3 0
500 http://ftp.de.debian.org/debian/ testing/main amd64 Packages
39.0.3 is the current version, but because the slots in unstable and testing are blocked by the esr-version, Sounds stupid, but isn't. unstable and testing are the internal distributions to develop the next stable, so having esr in testing and unstable make sense. so only experimental is left for the current release. Thats where the mozilla repository jumps in. So there is no good and no bad - the esr is conservative and fine with long term support, the current release is fine, beta and aurora is for people who are cool and don't do any useful work with the browser (aka web design or such things)
(sorry, devil
)
the beta and aurora versions are fine too - but have often problems with correct rendering, which make them not feasable for webdesign, but mostly for daily browsing - and the more people use them and report useful bugs (rendering, new implemented functionality and so on) the better the finally released version will be.