Navigator's adoption, particularly among corporate enterprises, suffered when Microsoft's Internet Explorer became an inseparable part of its operating system.
The non-settling states pursuing tougher remedies want Microsoft to make its media player code removable from the operating system, allowing PC makers to substitute rival products.
In court, states' attorney John Schmidtlein attempted to show that Microsoft was increasing the dependency of its media player on the operating system, even after the US District Court of Appeals two years ago faulted the company for "commingling" browser code with the operating system.
Will Poole, a Microsoft vice-president responsible for the Windows New Media Platforms Division, which builds media player for the operating system, returned to the stand to defend his company's actions.
Poole and Schmidtlein sparred over whether PC makers would install rival media players if they were not forced to take Microsoft's Windows Media Player.
"I believe our competitors will pay them [PC makers] not to carry it, Poole said. "They will weigh benefits between the payment they receive and the value they take out of the system."
At one point, he added: "I know of no good reason why they would take that technology out."
If Microsoft were forced to allow PC makers to add and subtract its media player code, Microsoft "would have to compete harder and innovate harder", Schmidtlein said.
Poole, however, said that if Microsoft's media player software code were removed the operating system would not support many rival media players.
Schmidtlein's line of questioning faced problems, particularly in regard to Windows XP Embedded, a version of the operating system used in devices such as cash registers that allows users to add and subtract "middleware" such as media players. The states are using XP Embedded to demonstrate that Microsoft can separate applications from its operating system.
Schmidtlein at one point asked Poole to give his best educated guess on an aspect of the embedded system's operation. Microsoft's attorney objected to a speculative answer and Judge Colleen Kollar-Kotelly agreed.
On the issue of commingling or codependency of code, Poole acknowledged under questioning that the codependency of its media player with the operating system was increasing, but he added that system design was being affected by the antitrust case. "We have certainly done our best to forecast where things might go," said Poole, referring to the antitrust case.
Linda Wolfe Averett, a unit product manager for Windows Media Player, followed Poole on the witness stand. Her testimony is intended to rebut Dave Richards, RealNetworks' vice-president of consumer systems, who testified as a witness for the nine non-settling states and the District of Columbia.
Richards had said in court that Microsoft's software licensing terms are "severe and onerous", and that they have harmed his company.
The non-settling states have refused to sign a Bush administration-backed settlement in the case. The judge is considering their remedies, which include forcing Microsoft to produce a stripped-down version of its operating system, carry Java, allow the porting of Office to other operating systems, and provide developers with access to the Windows source code.
Microsoft has three more witnesses to call: Jim Allchin, its group vice-president for the platforms division; Kenneth Elzinga, professor of economics at the University of Virginia, and John Bennett, a computing science professor at the University of Colorado.
Both sides are also expected to call rebuttal witnesses. The remedy phase could finish in two weeks' time.