After changing its stable release policy to a more accelerated pace, Mozilla released Firefox 5 pretty quick after the latest major Firefox version was put out. Firefox 4 was released on March 22, 2011 and this version follows only three months later.

Not long ago Mozilla changed the release cycle of Firefox, so that major new versions (Firefox 5, 6 and so on) will be released every 2-3 months. Currently, the latest alpha release is Firefox 6 Aurora, while the latest beta development version is Firefox Beta 5, which has made it into the Firefox Next PPA already.