Firefox 4 features a clean interface, competitive speed, HTML5 compatibility and two of the best browser features to be unveiled in a long time: the tab-wrangling prowess of Panorama, and the multicomputer synchronization power of Sync.
With Firefox 4, the "Chrome-ization" of the browser world is complete -- all of the major browsers now use a variation of the simple, stripped-down interface pioneered by Chrome.
The visual changes in Firefox 4 are quite substantial. Tabs now live along the top of the browser, above the address bar (which Firefox calls the "Awesome Bar"). Menus have vanished; to get at all of the browser's features, you click a button labeled "Firefox" at the top left corner of the browser and a menu drops down.
Firefox 4 may have borrowed some of Chrome's basic design ideas, but it has also introduced some useful new features as well. Key among them is Panorama, which helps solve the problem of tab proliferation. If you're the kind of person who tends to have many tabs open, making it hard to find the one you want quickly, Panorama may well be the best new feature of Firefox 4. Click the Panorama button (a square icon composed of four smaller rectangles) in the upper right of your Firefox window, and you'll come to a screen that shows thumbnails of all of your open tabs grouped in a single box against a blank background.
Firefox 4 introduces another feature, called Switch to Tab, to help you tame your tabs. As in the previous version of Firefox, when you type text in the address bar, Firefox searches through your history, previous searches and sites you've bookmarked and shows likely matches in a drop-down list below the address bar. Now, however, it also searches through any tabs you have open.
Firefox Sync can synchronize bookmarks, browsing history, passwords and open tabs.
Firefox 4 does an excellent job of supporting Web standards, including the upcoming HTML5 standards.