So let’s start off with the basics…
What’s new in Firefox 5.0?
At first glance, the GUI seems a little brushed up but no significant differences from the previous version of Firefox.

Mozilla have added a new button that when clicked on will “tells” websites not to track the user which isn’t really a big deal. Firefox 5 now supports CSS animations, which is good progress since it had to match up to Chrome, which already had this feature from a while back. Apart from these two features, there haven’t really been any other major changes. However, under the surface WebGL security has been tightened up, some tweaking has taken place to improve JavaScript performance and memory usage, consequently making life much easier for extension developers and. HTLM5 Standards support has been improved as well.
User Interface
Just like its predecessor, the Firefox 5 user interface doesn’t quite work on the Mac – in simple terms – it doesn’t really look nice compared to Chrome or Safari. Even applying themes won’t make a difference. On the other hand, on Windows-based PC’s it looks magnificent!
Nevertheless, whichever version you use, the user is provided with the ability to turn open tabs or “pin them” into App Tabs, which keeps key web-based services such as Gmail or Twitter visible without taking up too much space. The user can also organize app tabs into groups, which comes in very useful when carrying out research on multiple topics.
Mozilla had to mess this up by only allowing the user to save his/her Tab Groups by shutting down Firefox. Personally, I feel it would not only be more logical but provide a better browsing experience if one could save groups as with bookmarks.
As with its previous versions, Firefox has an address bar and a search box, although if you don’t type a URL the address bar takes you to a web search anyway – we’re already quite familiar with this though and it can’t really be improved.
The “Do not Track” button
I must admit that the guys at Mozilla have outdone themselves with this so kudos for them. By integrating this feature into their browser, Firefox is the first multi-platform to support this “Do not Track” system, which basically tells websites not to snoop on the user. When this feature is enabled, the browser sends messages in the form of an HTTP header to advertisers and other firms notifying them that they shouldn’t follow you when you are surfing on the Internet. The advantage of this is less behavioral targeting and a less likelihood of indirectly giving away your personal details. It is the perfect alternative to having to set “opt-out” cookies for every online snooper which as many of you are aware of would take a lot of time, something we lack of nowadays.

It’s so easy; it’s just a matter of ticking/unticking a box
Performance
SunSpider Javascript
The only way to determine how good a browser is, is to compare it against others and that’s what I did. I put 3 browsers to the test: Firefox 5, Chrome (latest version/build) and Safari 5 on a Sandy Bridge Apple iMac. When the results came up on the screen, the first thing that caught my attention was the fact that Firefox literally “zoomed” through the benchmarks in an incredible 200ms, faster than the 210ms for Chrome which was quite surprising. I had predicted Safari to end up in last place, and it did with 270ms. Conclusion: Apple still has a lot of work to do to match up to the other web browsers or even better, just forget about Safari and continue making iPhone’s, iPad’s and iMac’s.
The Acid3 Test
For those who don’t know what it is, it is basically a page from the Web Standards Project that checks the performance of a web browser regarding the issue of following certain selected elements from web standards, especially those associated to the Document Object Model (DOM) and JavaScript.
If the test is successful, the results of the Acid3 test will display a gradually increasing fraction counter with colored rectangles in the background. The number of subtests passed will indicate the percentage that will be displayed on the screen. I put Mozilla Firefox 5 through the test and the results are displayed below:

Even though the score stopped at 94 (on an iMac) or 97 (on a Windows PC), it proved to be stable and fast unlike Chrome 11 which clearly seemed to be “bugged” at least on OS X and displayed 100/100 solely to validate the test – nice try Google but you aren’t fooling me!

Internet Explorer 9 didn’t seem pretty bad either scoring 95/100 and Safari 5.0.5 which proved me wrong as I expected it to perform the worst out of the 4 web browsers with a surprising 100/100 (on an iMac – maybe that’s why!).
Firefox 5 extensions
Despite the soaring number of users who have switched to Chrome in the last months, Firefox still remains the best browser for geeks, control freaks and virtually anybody who wants their browser to be more than “just a browser”, more like a whole new browsing experience where almost anything can be done with the never-ending list of extensions that it has to offer. You heard me right, “never-ending”, the list goes on with all kinds of add-ins and tools that allow the user to customize their browser, i.e. web development tools, scripts to change the way sites look and behave, tools for online services and plugins for every imaginable task. No browser will be able to match Firefox in this aspect anytime soon, guaranteed! So rest assured, staff at Mozilla!

Believe it or not, Firefox still is the most expandable browser around, with add-ons and plugins for anything you can think of.
The Conclusion: “to download or not to download, that is the question?”
After a thorough analysis, it’s time I come clean and be honest: most of the improvements in this new browser are for add-on creators and web developers and there’s nothing really that would get end-users excited so let me put it to you this way: if you didn’t like Firefox 4, you will certainly NOT like Firefox 5. Whether you like it or not, it still doesn’t change the fact that it’s one of the fastest browsers currently available and no other browser (maybe Chrome up to some extent) can be a match for it in terms of expandability and freedom of customization.