With the upcoming changes in the beta and aurora channels (6.0 is going to reach beta, and 7.0 to reach aurora), the mozilla.debian.net repository is going to adapt, and drop versioned archives in favor of channel archives. The channel archives for beta and aurora already existed, however what is new is the “release” channel. Currently, that channel contains Iceweasel 5.0, but as soon as 6.0 is released, that’s what the “release” channel will contain.
To summarize, if you added lines containing
x is 4, 5, or 6 in your
/etc/apt/sources.list, you need to update it to the corresponding channel (don’t forget 4.0 is dead, you should use “release” instead).
iceweasel-6.0 archives still exist at the moment but will be dropped as soon as the new aurora and beta releases are ready, which should be real soon now (only waiting for actual upstream releases).
As a somehow related note, it should be noted that Iceweasel 5.0 should (finally) enter Debian unstable on the 15th of July, at which point the latest 6.0 beta will also be uploaded to Debian experimental. It is still unclear how long it will take for Iceweasel 5.0 to reach Debian testing/wheezy, because of all the reverse dependencies, but when that happens, we’ll also be able to push it to backports.debian.org.