So far, everything is uber fast and good looking (even though my favorite of favorite themes, Whitehart, looks crappy with the new layout and probably won't be updated. *sads*)
Of course the most notable change is that the tabs are now on top and they've now done away with the menu bar in favor of the Firefox button. I'm totally in favor of both of these changes.
I think the new layout definitely helps Personas. I've never really liked Personas (mostly because of Whitehart..., but also) because they never really made a big enough change, in my opinion. They were always covered up by the Address bar and whatnot. (You know what needs to exist? A "Transparent Address Bar" addon. That would be BA.)
The new layout and such is alot more compact, which is definitely a good thing. For the most part, I never really delv into all my menus and thus keeping them a few more clicks away is not really that big a deal.
One of the features I'm unsure of is the Panorama. It's interesting, for sure, but I'm still undecided as to if I think I will use it. (Of course the nice part about Firefox is that I'm not forced to use it. Yay, freedom of choice!) Basically you can group your tabs into different...er....groups, and then switch through them. This lets you have many tabs open, but only have to focus on several ones at a time. It gets its name from a button that lets you zoom out, much like some of the Compiz effects or
App Tabs are something I'm very excited about. The concept is that if you want to have a tab open all the time, you can shrink it down to just the favicon, so it will take up barely any space and not have a close button. Plus, App Tabs will glow when something changes in them, so it's uber useful for tweets in Twitter or mail in Gmail. Lastly, App Tabs basically become a part of your home page, more or less, because they always appear when you start Firefox.
Firefox Sync really isn't a new feature, just because it was an Addon for 3.6.*. It is a nice feature for sure, just nothing new for me. (Speaking of sync, I do have exciting news I just discovered...)
Integrating the "Addons" page into a tab is definitely welcomed....even if it was taken from Chrome. Although they promise that you won't have to restart, I've already had to several times, but I suppose it is for "old" addons.
I'm not really one for benchmarks and tests, but this Firefox is significantly faster than 3.6 or 3.5, and according to Wiki, it scored 97/100 on the Acid3.
The last "feature" is the "Do not track" setting. If you want to read more about it, click here, but the basic gist of it is that Firefox will send a DNT header with each page request. The website you're going to then has a choice: it can comply to that header, or it can track you anyway (i.e., place a personalized ad). In essence, it's a way to give websites the chance to do the right thing on their own. But this is money we're talking about, and I'm not so sure it's going to work out so well. I do give Mozilla their props for at least making an effort, and I believe their heart is in the right place, since they've also said:
[Do not track] will require collaboration across the entire ecosystem...and once defined, we will ship that solution as part of Firefox.I really don't see it as a big deal either way since I'm pretty sure there are other ways to prevent tracking such as NoScript and I use DuckDuckGo which doesn't allow sites to track me. But I do hope this whole Do Not Track feature will gain traction. The fact that IE9 decided to pick it up too will hopefully help...or hurt, deciding on how stupid Microsoft decides to be with it.
In any case, I'm very excited for this new version of Firefox. Maybe it was just the release of Chrome, but 3.6 seemed a tad outdated...usable, but outdated. Firefox 4 really seems like a breathe of fresh air, and hopefully that's not just the initial impression.
Go. Get it. Now.
PS - I can barely believe it, but I've already seen the Chrome fanboy in the comments section on an article about Firefox 4 and it's features. I know that fanboys exist everywhere....but seriously, this is ridiculous. The Internet Explorer team sent the Mozilla team a cake for the release of Firefox 3. If the developers of web browsers are friendly to one another, why should the users be hostile?
The thing that gets me is that Chrome users act like discussing Firefox 4's new features is insulting to Chrome. It's not. It's like "Hey, here's Firefox 4." Nobody's saying that everyone should use Firefox 4. Nobody's even saying it's better than Chrome. Just let us pat Mozilla on the back, use whatever browser we want, and we can all live in harmony. (Too much to ask?) Overally, grow up.