Microsoft's Internet Explorer and Mozilla Foundation's Firefox are the two most popular browsers in the world. A few years after the open source Firefox browser was introduced, it has successfully chipped away at IE's monopoly.
The first version of Internet Explorer (IE) was released in August 1995, a time when Netscape had a near monopoly in the browser market. IE was bundled together with the dominant Windows operating system and by 2001 had a monopoly market share of over 90%.
Dave Hyatt and Blake Ross began working on the Firefox project as an experimental branch of the Mozilla project. They believed the commercial requirements of Netscape's sponsorship and developer-driven feature creep compromised the utility of the Mozilla browser. To combat what they saw as the Mozilla Suite's software bloat, they created a stand-alone browser, with which they intended to replace the Mozilla Suite. On April 3, 2003, the Mozilla Organization announced that they planned to change their focus from the Mozilla Suite to Firefox and Thunderbird.
From 2005 to 2010, Firefox had been steadily gaining market share from Internet Explorer. Wikipedia states that IE's market share in 2007 was 78.6% and around 75% in Jan 2008.  This includes all versions of IE. Firefox had close to 20% share in 2008. By June 2010, Firefox share was 31% and IE was down to 50%. In August 2011, Firefox share was around 23% and IE's share was around 38%.
In June 2012, the desktop browser market share of Internet Explorer and Firefox relative to other browsers was as follows:
|StatCounter||32.76 %||32.31%||24.56 %||7.00 %||1.77 %|
|Diffen.com (includes mobile)||23.4%||27.2%||17.6%||21.6%||2.5%|