While App Tabs can be used with any open tab, this feature is meant for websites that you might keep open throughout the day, like Pandora, Twitter or Gmail.
The transformation is so complete that Mozilla appears to have beaten back the sudden onslaught of competition in the form of IE9. It may even triumph over Chrome 10 — but that fight’s one to watch closely.
“Panorama” feature gives users the ability to group tabs together into manageable groups, which can be named, organized and edited simply.
noticeable default change to the Windows version of Firefox 4 is the “Firefox button,” or the browser menu, which has been reduced to a small orange button that appears in the top left corner of the browser.
The most noticeable difference between Firefox 3.6 and 4 is the speed