One of these features is the "Type Inference capability". It is a new JavaScript system and the object is to analyze variables.
Another feature that help Firefox 9 to be more rapidly XHR chunking. XHR is commonly used as an Ajax-type web request for dynamic data. By chunking XHR, the browser experience gets faster as users don't have to wait for all the data to be transmitted.
Firefox 9 respects user's choice and makes it even easier for websites to choice to be tracked or not. Mozilla implemented "Do Not Track in Firefox 4" feature that provides both Web users and advertisers with a mechanism to opt in or out of behavioral tracking and other online data collection.
Firefox 9 is also available for Android phone and tablet users as well. Firefox 9 introduces a new tablet user interface.