Chicago (IL) – Firefox 3 is approaching is completion date with the third beta version being published this year. The latest release, Beta 5, shows improved integration into Windows, Mac OS X as well as Linux and has received a substantial speed boost.

Mozilla said that it has made changes to the browser’s JavaScript engine and has applied profile guided optimizations to accelerate the display of webpages. Compared to Firefox 2, certain web applications such as Google Mail and Zoho Office “run twice as fast in Firefox 3 Beta 5,” according to the developers. Mozilla claims that the most recent Beta is also faster than previous releases.

Under the hood, the new Beta apparently has received improvements in connection parallelism, according to Henrik Gemal, a systems engineer at TDC Mobil a Mozilla contributor. Firefox now supports six connections per host (up from 2) and matches Internet Explorer 8 in this discipline, Gemal wrote on his blog. The maximum number of HTTP connections has increased from 24 to 30 while the number of HTTP connections per host jumped from eight to 15.

“All in all this will make Firefox 3 beta 5 even faster,” Gemal wrote.

The release notes of the new browser noted that version 5 includes more than 750 changes from Beta 4, which was released not even a month ago. Part of those changes is new Windows icons and native user interface widgets in the browser and in web forms. On the Mac, Firefox has received a new theme that makes the browser look more like a native Mac OS X application. Under Linux, Firefox’s default icons, buttons, and menu styles now use the native GTK theme. There was no information on a release date of the final version.

You can download Firefox 3 Beta 5 here.