First it’s Windows. Now it’s Internet Explorer.Already facing a threat to its Windows operating system dominance from the open source Linux platform, Microsoft can’t be too thrilled to find out this week that its Internet Explorer browser is losing market share to the open source Mozilla offering. After holding at 95 percent of the market for years, share has dropped to 92.9 percent as of October. This can’t be good news for a company whose grand entrance into the browser market and the bundling of Internet Explorer with Windows several years ago displaced Netscape as the dominant browser. Although 92.9 percent still is quite an overwhelming share, the concept of open source continues to present new burdens for the Redmond, Wash. software giant. Open source is creating new dynamics in the software marketplace, which will force companies like Microsoft and Sun Microsystems to keep innovating in both technology and business models. Microsoft founder Bill Gates, when questioned a few weeks ago about Linux, had kind of a carefee attitude about the platform, noting that IBM’s OS/2 was supposed to be a Windows killer, too. Now, he or other Microsoft executives also will have to assess how serious a threat Mozilla and open source is to their browser reign. Technology Industry