On February 15, 2005, Microsoft announced that Internet Explorer 7 would be available for Windows XP SP2 and later versions of Windows by mid-2005. The announcement introduced the new version of the browser as a major upgrade over Internet Explorer 6 SP1.
Opera had been a long-time small player in the browser wars, known for introducing innovative features such as tabbed browsing and mouse gestures, as well as being lightweight but feature-rich. The software, however, was commercial, which hampered its adoption compared to its free rivals until 2005, when the browser became freeware. On June 20, 2006, Opera Software released Opera 9 including an integrated source viewer, a BitTorrent client implementation, and widgets. It was the first Windows browser to pass the Acid2 test. Opera Mini, a mobile browser, has significant mobile market share. Editions of Opera are also available for the Nintendo DS and the Wii.
Microsoft released Internet Explorer 7 on October 18, 2006. It included tabbed browsing, a search bar, a phishing filter, and improved support for web standards (including full support for PNG) — all features already long familiar to Opera and Firefox users. Microsoft distributed Internet Explorer 7 to genuine Windows users (WGA) as a high-priority update through Windows Update. Typical market share analysis showed only a slow uptake of Internet Explorer 7 and Microsoft decided to drop the requirement for WGA and made Internet Explorer 7 available to all Windows users in October 2007. Throughout the two following years, Microsoft worked on Internet Explorer 8. On December 19, 2007, the company announced that an internal build of that version had passed the Acid2 CSS test in "IE8 standards mode" — the last of the major browsers to do so. Internet Explorer 8 was released on March 19, 2009. New features included accelerators, improved privacy protection, a compatibility mode for pages designed for older browsers, and improved support for various web standards. It was the last version of Internet Explorer to be released for Windows XP. Internet Explorer 8 scored 20/100 in the Acid3 test, which was much worse than all major competitors at the time.
On October 24, 2006, Mozilla released Mozilla Firefox 2.0. It included the ability to reopen recently closed tabs, a session restore feature to resume work where it had been left after a crash, a phishing filter, and a spell-checker for text fields. Mozilla released Firefox 3.0 on June 17, 2008, with performance improvements and other new features. Firefox 3.5 followed on June 30, 2009, with further performance improvements, native integration of audio and video, and more privacy features.
On December 28, 2007, Netscape announced that support for its Mozilla-derived Netscape Navigator would be discontinued on February 1, 2008, suggesting its users migrate to Mozilla Firefox. However, on January 28, 2008, Netscape announced that support would be extended to March 1, 2008, and mentioned Flock alongside Firefox as alternatives to its users.
During December 2009 and January 2010, StatCounter reported that its statistics indicated that Firefox 3.5 was the most popular browser, when counting individual browser versions, passing Internet Explorer 7 and 8 by a small margin. This was the first time a global statistic has reported that a non-Internet Explorer browser version had exceeded the top Internet Explorer version in usage share since the fall of Netscape Navigator. This feat, which GeekSmack called the "dethroning of Microsoft and its Internet Explorer 7 browser," could largely be attributed to the fact that it came at a time when version 8 was replacing version 7 as the dominant Internet Explorer version. No more than two months later Internet Explorer 8 had established itself as the most popular browser version, a position which it still held as of March 2011. And other major statistics, such as Net Applications, never reported any non-Internet Explorer browser version as having a higher usage share than the most popular Internet Explorer version, although Firefox 3.5 was reported as the third most popular browser version between December 2009 and February 2010, to be replaced by Firefox 3.6 since April 2010, each ahead of Internet Explorer 7 and behind Internet Explorer 6 and 8.