The first browser wars saw Microsoft's Internet Explorer devour and digest the once-great Netscape browser. In the ten years since then, the various versions of IE have maintained a steady dominance across the market. It's only been over the last few years that serious challengers have started to arrive. Google's Chrome browser and Mozilla's Firefox have both risen up to compete with Internet Explorer.
In fact, they're doing more than just competing. They're winning. In March 2009 the combined market share of IE6, 7, and 8 was 65.8%, a commanding lead. But now, just three months later, Internet Explorer's overall share has dropped to 54.4%.
That's a huge loss to bear, and it's due in part to the recent spate of upgrades among IE competitors. In that three month timeframe Firefox 3.5, Google Chrome, and Apple's Safari 4 all launched. It's entirely possible that within the next three months we will see Firefox 3.0 (or Firefox 3.5) actually beat Internet Explorer's top version in total market share and become the dominant web browser.
Internet Explorer 8 is doing very well, and has shown a 16.7% growth since its launch in March. IE 8 could end up edging out Firefox for dominance and maintaining the Microsoft status quo. Even if that happens, I think IE's overall losses are still unlikely to reverse. It looks like users who switch away from IE browsers rarely come back. Unless Microsoft is able to really innovate with the next edition of IE I think we're going to see this trend continue.