From the ashes of Netscape Navigator and the Mozilla Suite came Mozilla Firefox in 2004 (then known as Mozilla Phoenix, followed by Mozilla Firebird). Although a tiny browser back then, it was heavy on awesomeness! While it was not the first browser supporting tabbed browsing, it was the first browser that took any measurable market share from Internet Explorer and made tabbed browsing popular. Along with the tabbed browsing came extensions.
Also present with Mozilla Firefox is better support for Web Standards, which allow web designers to design better webpages without having to resort to undocumented functionality or hacks. Mozilla Firefox also boasts better security than its main rival Internet Explorer does. With less vulnerabilities discovered and less exploits released for Firefox, this is a browser to consider!
Apart from these features, there are countless add-ons for Firefox that add or modify features in unimaginable ways. You will be surprised to find extensions and add-ons in Firefox for things and purposes you have never imagined. Make your way to Mozilla's add-ons site to browse the extensions and choose the ones you find useful. A word of caution though! Do not install too many add-ons or your browser will slow down and eat up lots of memory.
Download Mozilla Firefox.