With Google's Chrome browser surging in popularity, one would be forgiven for thinking that Firefox was about to get leapfrogged. Nah, son. Hours after releasing its all-new Firefox 4, Mozilla has clocked well over two million downloads of the web's second most popular browser.

Released a week after Microsoft let loose the revamp of its own browser, Internet Explorer 9 (still the web's #1 browser), Firefox 4 introduces a number of changes both aesthetically and technically, that should place back in the running with its competitors. It's the biggest overhaul of the browser in years.

The user interface has been streamlined, doing away with menu bar. On Windows, a Firefox drop-down menu takes its place, on Mac, it just looks like Google's Chrome browser, or Opera.

There's a new plug-in architecture called JetPack, a new, faster JavaScript engine, and better HTML 5 support. A new "Tab Groups" feature lets users group together tabs so their windows don't become overrun with too many windows. If you're worried about your add-ons, well, you should be. Mozilla says that as of now, more than 70% of its add-ons are compatible with Firefox 4. There's also a new Add-On Manager that helps you managed all of them and find new ones, and a host of other cool features. 

According to Mozilla's download counter, there will probably be 3 million downloads by the time you read this.

Download it here for Mac OS X, Windows, and Linux.

[via PC Mag]