I've put Firefox 4 through its paces for a Computerworld review, and I was extremely impressed. Here are four reasons to love the latest version of the browser.
Panorama
I spend most of my day with multiple tabs open, and very quickly lose track of them. Panorama solves the problem --- it's the best tab-wrangling feature I've ever seen in a browser.
With it, when you have a lot of tabs open, you put them into separate groups, such as news, technology, entertainment, and so on. Then, when you use one group, all of the other tabs in all of the other groups are hidden. It's easy to switch to other tab groups. It's one of the biggest browser productivity-boosters I've ever used.
Lean interface
Firefox was beginning to look old and dated --- no surprise, given that the last big update, 3.5, was released two years ago. In this version, Firefox follows Chrome's lead with a "less-is-more" approach to design. Menus and navigation have been scaled back and eliminated, so that Web content gets more screen real estate, and is front and center.
Firefox Sync
With this nifty feature, you can keep your bookmarks, history lists, and so on automatically synchronized among multiple computers running Firefox on multiple operating systems. When the final version of the Android version of Firefox is released, it will work there as well.
Firefox Sync will even let you see what tabs are opened in other browsers, and open them in the browser you're currently using.
Many small extras
There's been a lot else that's useful in the new version of Firefox as well, including more screen real estate for the Add-On Manager, a Switch-to-Tab feature that lets you search across multiple tabs, and some improved security.