Both Mitchell Baker, the former CEO of Mozilla and the chairwoman of Mozilla Foundation, and Harvey Anderson, Mozilla's chief counsel, posted lengthy blogs, citing concerns with Microsoft's proposal and spelling out changes they want to see.

John Lilly, Mozilla's current CEO, confirmed that the messages from Mitchell and Anderson were part of a company-wide plan. "It's part of our effort to get across our point of view," he said in an interview. "In principle, [Microsoft's proposal] sounds good, but in practice, the way they implement it will make a big difference."

Mozilla's top executives were reacting to a July 24, when it told Brussels-based antitrust officials that it would give Windows users a chance to download rivals' browsers.

A key part of that plan would be a that EU Windows users would see if IE was set as the default browser. Under Microsoft's proposal, the ballot will offer links to downloads of Mozilla's Firefox, Apple's Safari, Google's Chrome and Opera Software's Opera.

In January 2009, the European Commission filed charges against Microsoft, accusing the company of shielding IE from competition by including it with Windows. Since then, Microsoft has made several moves, including offering a in Windows 7 that lets users disable IE, to fend off fines and even tougher antitrust actions against its software.