Days after Microsoft unveiled the first beta version of its upcoming Internet Explorer 8.1, Mozilla released the fourth beta of Firefox 3.

According to Mozilla, the new beta offers more than 900 enhancements and especially improvements to performance and memory usage.

In addition, the Beta 4 includes fixes for stability, platform enhancements and user interface improvements.

Compared to Firefox 2, web applications like Google Mail and Zoho Office run twice as fast in Firefox 3 Beta 4, and the popular SunSpider test from Apple shows improvements over previous releases, Mozilla noted.

For example, Firefox 3 Beta 4 integrates a revised download manager which makes it much easier to locate downloaded files. Now the users can see and search on the name of the website where a file came from. Also, active downloads and time remaining are always shown in the status bar as the files are download.

Another feature is resumable downloading, that means the users can now resume downloads after restarting the browser or resetting the network connection.

Firefox 3 Beta 4 also features a new location bar and auto-complete capability. Now, a user can type in all or part of the title, tag or address of a page to see a list of matches from his history and bookmarks: a new display makes it easier to scan through the matching results and find the needed page. Results are returned according to their frecency (a combination of frequency and recency of visits to that page) ensuring that the user is seeing the most relevant matches.

The beta of the new browser is available here. Mozilla announced it plans to release at least a new beta, Beta 5, before Firefox 3 will hit the release candidate stage.