I have been using the Mozilla Firefox, for almost a year now. I installed it as it was said to be faster than IE (i was on IE6 earlier). I think the performance of any internet related software(like browsers, IM clients etc) depends on the internet connection speed, Iam on a 64KBPS connection from Sify(you may want to read my review on Sify https://mouthshut.com/review/Sify_Broadband_Internet_Connection-98492-1.html). I am using version FireFox Ver 1.5.0.3, and heres what I think of it.
The best thing about firefox is tabbed browsing, it lets you view more than a single website in the same window. This feature is the biggest plus if you compare it with IE6, which is what most regular users use. With tabbed browsing you save time spent on moving through different browser windows, not to mention the precious taskbar space saved :), but then IE7 has tabbed browsing too and so does Opera(Opera claims to be the fastest browser on the planet).
Another thing I like about Firefox is its built in search box. Apart from the built in search engines you can add other engines like webster, imdb etc. This saves time spent on going to a search site first and then searching, but then again the same features are available on IE7 and Opera.
Apart from the above two features firefox is said to be a lot safer than IE, well they keep releasing updated versions ever so often so Iam not sure about the claim on safety. If it is all that safe then why release updates with security patch all the time like Microsoft does?
Another good thing about firefox is the wide variety of themes and add ons for firefox.
Is firefox faster than IE? Just a bit, it loads icons and buttons faster than IE (for eg. on Yahoo Mail), but then the Javascript(which gives functionality to those buttons) takes almost as long as IE.
One major problem is that you need to install plugins for stuff like flash, java etc. Opera doesnt need a separate plugin to installed for Java if you already have it installed for IE.
Verdict: Firefox is part of a movement against Microsoft’s domination of the Internet, when it was first released it had path breaking features. However, others have caught up now. Firefox is bundled in Google Pack(a collection free software supported by Google, it includes software like Ad-Aware & WinZip apart from firefox). Try Firefox if you want to(for the addons), but it isnt as path breaking as it used to be. Opera is just as good if not better, IE7(https://microsoft.com/windows/ie/default.mspx) is also a good browser.