If you use Firefox nightly builds, and you had the Jetpack Prototype installed, you might have noticed that about two weeks ago, your jetpacks had started to get disabled a short while after you had opened your browser. This issue was really frustrating, since some of us run jetpacks which are very important in our daily work.
I filed bug 554169 about this issue. Paul O'Shannessy fixed this, and earlier this week, the Jetpack team released a new version of the Jetpack Prototype which fixes this issue. You can install it from AMO, and your jetpacks will resume working reliably on nightly builds.