To see how it would do I've been running the Firefox 4 betas, release candidates, and just now the final, on Windows 7 SP1, Windows XP SP3, and the Mint 10 Linux distribution. For XP and Windows 7, I used a Gateway SX2802-07 desktop. This PC uses a 2.6GHZ Intel Pentium Dual-Core E5300 processor and has 6GBs of RAM and a 640GB hard-drive. For my Linux Firefox box, I used a Dell Inspiron 530S powered by a 2.2-GHz Intel Pentium E2200 dual-core processor with an 800-MHz front-side bus. This box has 4GBs of RAM, a 500GB drive. This is what I found.
1. Operating System and Application Interoperability
If there's anything you want to do with a browser, but it's not built-in, there's almost certainly a way to do it with a Firefox extension. I found that most of the extension I use every day with Firefox, such as the newest versions of the LastPass password manager; the Xmarks bookmark manager; and the Google toolbar work just fine with Firefox 4.
Not all add-ons will work so smoothly though. There have been many changes in how Firefox handles extensions. I know some extensions will fail until they've been updated. I was also annoyed to find that I had to close and restart Firefox to get most extensions to work.
Speaking as a user Chrome still feels faster to me, followed by IE, and then, I'm sorry to say Firefox. Still, Firefox 4 feels much faster than Firefox 3.6x. Your usage may vary.
I was also pleased to see, after multiple hours of use and many tabs opened and closed, that Firefox finally seems to have fixed its infamous memory leak problems. This often led to system slowdowns, and in extreme cases, even to crashes. That, knock on silicon, now seems to be a thing of the past.
3. Web Interoperability
Firefox 4 does a much better job than IE 9 when it comes to Web standards compatibility. On the Acid3 Web standards test, Firefox 4 came in with a score of 97 compared to IE 9's 95. On the HTML 5 compatibility test, Firefox had a good score of 255 compared to IE's 130. Unfortunately, Chrome does better than both. Chrome had an Acid 3 score of 100 and a HTML 5 mark of 288.
In practice, I didn't find any Web pages-except for those sad sites still stuck in IE-6 comparability hell-that gave Firefox 4 any problems.
Page 2: [Features and Problems] »
Features and Problems
There are a lot of features to like in Firefox 4. A very short list of the ones I like includes Firefox Sync. If it could work across browsers, it might replace my current bookmark and password favorites: Xmarks and LastPass. If you don't change browsers though, Firefox Sync might be all you need.
I also like tab grouping. This, like the name suggests, lets you group tabs together. It's perfect for keeping tab 'families,' like say one group for "social networking" and another for work.
A related feature, which I'm already fond of, is Firefox's ability to turn Web pages into pinned "applications". All you need do is right click on a tab to turn it into an application, and, until you change your mind, the page will always be available when you start your browser. This is ideal for pages such as Gmail that you know you'll be opening over and over again during the course of the day
5. And what's wrong
Firefox is full of good stuff, but even taken all together is it good enough to bring back users who have moved on to Chrome, or back to IE? I don't think so.
It is faster than it once was. It is better than it once was. It has many new and useful features. But, it's in a dead-heat with the other browsers when it comes to speed. And, yes, it is better, but then so are the others. As for the features, many of these, such as pinning, were already available in other browsers.
I'll also add one possible problem. I happen to like the Chrome-style of a minimal Web browser interface. Now that everyone, including Firefox, is copying it though I really wonder if it's this clean interface is for everyone. I suspect a lot of people like having the controls easily available lined up on the top of the program even if they do use up some of screen real-estate.
Had Firefox shown up on time, in 2010, it might have been a different story. Today, though, I fear it's a case of too little and too late for it to be a contender in 2011. I see Firefox continuing its slow decline to the rise of Chrome in users hands, while IE 9 will, for a time at least, will stabilize IE's generally declining market share. Eventually, I foresee Firefox becoming the number three Web browser with IE and Chrome fighting for the top prize.