This week, six weeks after the release of Firefox 4 beta 10, Mozilla Firefox 4 has left the beta stage and is now in the Release Candidate phase.

The release of the RC release represents significant performance enhancements, including smaller memory footprint, crash protection, faster graphics rendering and faster page loading. In addition, there are some distinct usability-improving features already spotted on the new minimalist UI of Firefox 4. Let’s take a quick look at them:

1. App Tabs

Users can turn any tab into an App Tab by right-clicking on it and selecting “Pin as App Tab.” These tabs can be found in the upper left-hand corner of the browser, beside the browser tabs that are now placed by default above the search bar instead of below it.

Alex Faaborg, the principal designer on Firefox, explained that the advantages of this new arrangement are more logical visuals, space efficiency, accommodation of the new App Tab feature and a redesigned notification window that associates the notification with its site’s tab.

2. Switch to tab

When the user starts typing the address of a website that is already open in a tab, Firefox 4 will suggest an option to switch to that tab. This feature’s really helpful for users who open more tabs than they can remember.

3. Firefox sync

Firefox now has the ability to sync bookmarks, browsing history, passwords, form fill data, and open tabs across multiple computers and smartphone.

4. Firefox Panorama

Described as “a more panoramic view of your tabs,” Panorama allows you to overview all of your tabs and organize them into groups using a drag and drop interface.