As part of the ongoing work to move our Betas and Release builds to our new update server, I’ll be landing a fairly invasive change to it today. Because it requires a new schema for its data updates will be slightly delayed while the data repopulates in the new format as the nightlies stream in. While that’s happening, updates will continue to point at the builds from today (June 16th).

Once bug 1026070 is fixed, we will be able to do these sort of upgrades without any delay to users.

http://hearsum.ca/blog/june-17th-nightlyaurora-updates-of-firefox-fennec-and-thunderbird-will-be-slightly-delayed/