It's the same as Chrome's - 6 weeks. What I think made a lot of people before attack Mozilla for it was because: 1) the "Firefox user" wasn't used to this kind of fast updates, the way the "Chrome user" was - and 2) Firefox' updates were not silent, and therefore you knew you got an update and some users may have been getting annoyed having to update it so often, instead of silently upgrading in the background. But apparently they now have silent upgrades starting with this version.