I am playing with the 64 bit version on Ubuntu Karmic and so far is seems pretty great. You can grab a copy here and, once unzipped into a directory you can run it by doing
chmod +x firefox
I am also excited by the new Add-ons manager. Mozilla is taking things that typically open a new window and making them run in a new tab instead. This is excellent since the Add-ons definitely require more space than the dialog they were appearing in allowed for. Its interesting that for all the seeming obviousness of the tabbed window design and how long its been around, browser makers are still working on fully integrating the concept into the browser.
My only disappointment so far is likely not an issue with Firefox at all. When I first saw the mockups I was excited to see that Mozilla was following Chrome’s lead in moving the tabs into the otherwise underused title bar. While I love the screen real estate that Chrome gives, it hasn’t been enough to tempt me away from all the amazing plugins that Firefox has.
Version 4 was supposed to mean that I got to have my cake and eat it too, adding the look of Chrome to the browser I already use.However while Windows users get the Chrome like interface, on Linux they have merely simulated the effect by hiding the bookmarks toolbar. Irritatingly, the Windows 32bit version gets the full treatment, tabs on top, File, Edit and Bookmarks all hidden away until you hit the ALT key. Its pretty sexy.
Disappointing but my suspicion is that it likely has something to do with the way windows are handled by Gnome, rather than anything to do with Firefox. Hopefully that will be sorted out with Gnome 3. For the moment, fast is good enough.