I like how the Mozilla team is speeding up updates, but I dislike the fact that they decided to use 5.0, 6.0, 7.0, etc...
Point releases like 3.6 were considered a major release in the past, so using numbers like 4.1 and 4.2 would have made much more sense, especially for those who aren't aware of what's going on and would expect lots of changes with a jump from 4.0 to 5.0. In fact, there really aren't many changes at all and most (if not all) are things most users would not care about or even notice.
Versions like 5.0, 6.0, 7.0 should be reserved for the truly big updates, like major new features (such as the Panorama feature introduced with 4.0) and interface changes.