Mozilla Firefox

Microsoft's head of Australian operations, Steve Vamos, stated in late 2004 that he did not see Firefox as a threat and that there was not significant demand for the feature set of Firefox among Microsoft's users. Microsoft Chairman Bill Gates has used Firefox, but has commented that "so much software gets downloaded all the time, but do people actually use it?"

A Microsoft SEC filing on June 30, 2005 acknowledged that "competitors such as Mozilla offer software that competes with the Internet Explorer Web browsing capabilities of our Windows operating system products." The release of Internet Explorer 7 was fast tracked, and included functionality that was previously available in Firefox and other browsers, such as tabbed browsing and RSS feeds.

Despite the cold reception from Microsoft's top management, the Internet Explorer development team maintains a relationship with Mozilla. They meet regularly to discuss web standards such as extended validation certificates. In 2005 Mozilla agreed to allow Microsoft to use its Web feed logo in the interest of common graphical representation of the Web feeds feature.

In August 2006, Microsoft offered to help Mozilla integrate Firefox with the then-forthcoming Windows Vista an offer Mozilla accepted.

In October 2006, as congratulations for a successful ship of Firefox 2, the Internet Explorer 7 development team sent a cake to Mozilla.As a nod to the browser wars, some readers joked about the cake being poisoned, while others jokingly suggested that Mozilla send a cake back along with the recipe, in reference to the open-source software movement. The IE development team sent another cake on June 17, 2008, upon the successful release of Firefox 3.

In November 2007, ASMS employee Jeff Jones criticized Firefox, claiming that Internet Explorer experienced fewer vulnerabilities and fewer higher severity vulnerabilities than Firefox in typical enterprise scenarios. Mozilla developer Mike Shaver discounted the study, citing Microsoft's bundling of security fixes and the study's focus on fixes, rather than vulnerabilities, as crucial flaws.