Review:
Firefox 5 is the first version of Firefox released under Mozilla's rapid-release cycle, which means that instead of seeing a new whole-number version once every year or two, you'll now see one every three months. This follows in the footsteps of Google Chrome, which adopted the rapid-release cycle a while ago and is now up to version 12 (at the time this review was written) despite having its first release only in 2008.
Firefox 4 had a massive impact on Firefox 5, and so this review is not dramatically different from its predecessor. Firefox 4 had a rough time in its early development, but those days are over. The browser that you can download now is in the same speed category as its competition; offers many similar features (stronger in many areas and slightly weaker in others); includes broad, cross-platform support for hardware acceleration and other "future-Web" tech and standards; and is a must-have for Android users (download for Android).
In Firefox 5, you get more incremental updates that generally focus on making the browser work better. One of the most important improvements is that the browser now supports Mozilla's new Add-on SDK, formerly called Jetpack. This foundation lets programmers build extensions out of Web technologies such as HTML, CSS, and JavaScript rather than the older XUL technology. Extensions are expected to be easier to write and ought not to break when new browser versions arrive, although add-on developers must still decide whether to rewrite their existing extensions. The browser supports Mozilla's new Add-on Builder, too, which ought to make it easier to create add-ons.
Source : Mozilla Firefox for Mac - Free software downloads and software reviews - CNET Download.com http://download.cnet.com