An awesome web browser from Mozilla. It was originally derived from Mozilla's (Seamonkey) code, but now has plenty of coding of its own. It supports W3C's standards and is quite secure. Best of all, it doesn't have support for Microsoft's security hole (read: gate for hackers to enter your computer) known as ActiveX, nor does it have most of the problems Internet Explorer has.
Mozilla will pay anyone $500 bucks for volunteering to fix security holes in its software, which is free (yes, as in speech, but also as in beer). That's pretty generous.
Incredibly good browser overflowing with useful features from the good folks at Mozilla. Tabbed browsing, a near-impenetrable popup blocker and general awesomeness compounded by the fact that you can add just about any feature you want using Firefox's plugin support make for a browser that simply trounces anything else.
The only flaw is the name. They ought to call it Firebox because that'd be seriously awesome.
I can't believe how utterly awesome Firefox is. And yet, if only it were named Firebox, it might be ten times awesomer.