Firefox 2 is in beta currently, beta2 release candidate 2. So that means it's going to be some weeks before v2.0 goes gold for public consumption. I was a little hesitant about installing the beta, knowing that in the past upgrading Firefox has brought with it bugs and certainly shut off popular extensions.
What most attracted me to it was whispers that the memory leaks have been greatly reduced, and performance improved. Firefox (originally Phoenix) started out as a nice stripped down version of Mozilla. Then gradually, it accepted so many features that it became rather heavy, especially on slower machines. It is a good thing that performance is being addressed continually, even though I doubt Firefox will ever match up to Opera in that regard. I haven't run any benchmarks to verify, but the new Firefox does seem a little faster. Noticeably, scrolling is faster.
A welcome new addition is a built-in session saver. I have been using the SessionSaver extension since the dawn of man basically, finally it is a built-in feature. When you close Firefox (or it crashes), it will restore your tabs and pages opened in them (new option in the settings).
Tab handling has improved. Every tab has a close icon, but you can also close tabs by middle-clicking on them. I thought this was a bug to begin with, I accidentally closed a window while filling in a form, but it's just a quick way of closing tabs. If you do close a tab accidentally, use History > Recently Closed Tabs to bring it back.
A new feature is a built-in spell checker (supporting a range of languages) for all form input. It highlights typos as you write, with the familiar red underline. While this isn't something I consider a major breakthrough, I'm sure a lot of people will love it.
Finally, a bug fix. in Firefox1.5, when you have the bookmarks drop-down menu open and you scroll with the mouse wheel, it will cycle between tabs. In Firefox2, it does the logical thing - scrolls the drop-down menu.
Extension wise, Adblock and Flashblock both work, Dictionary lookup doesn't yet.
September 7th, 2006