Late last week we discovered the expiration of the GPG key that we use to sign Firefox, Fennec, and Thunderbird nightly builds and releases. We had been aware that this was coming up, but we unfortunately missed our deadline to renew it. This caused failures in many of our automated nightly builds, so it was quickly noticed and acted upon.
pub 4096R/0x61B7B526D98F0353 2015-07-17 Key fingerprint = 14F2 6682 D091 6CDD 81E3 7B6D 61B7 B526 D98F 0353 uid Mozilla Software Releases
sub 4096R/0x1C69C4E55E9905DB 2015-07-17 [expires: 2017-07-16]
The new primary key is signed by many Mozillians, the old master key, as well as our OpSec team's GPG key. Nightlies and releases will now be signed with the subkey (0x1C69C4E55E9905DB), and a new one will be generated from the same primary key before this one expires. This means that you can validate Firefox releases with the primary public key in perpetuity.
We are investigating a few options to make sure key renewal happens without delay in the future.