The Commission, Europe's top antitrust authority, charged Microsoft last month with distorting competition in the market for web browsers by bundling in its Internet Explorer (IE) browser with the Windows operating system.
If the charges stick, then Microsoft could be forced to change the way it distributes IE, as well as pay a fine for monopoly abuse.
Mitchell Baker, Mozilla's chairperson, said in a blog that appeared over the weekend that she wanted to offer Mozilla's expertise "as a resource to the EC as it considers what an effective remedy would entail".
She said there isn't "the single smallest iota of doubt" that Microsoft's tying of IE to Windows "harms competition between web browsers, undermines product innovation and ultimately reduces consumer choice".
Mozilla has been granted what's called 'interested third party' status in the case, which allows it to submit arguments to the European regulator, to see the confidential statement of objections the EC sent Microsoft last month, and to participate in a face-to-face hearing if Microsoft requests one.
However, it isn't a complainant in the case. That role goes to Norwegian web browser developer Opera, which complained to the EC just over a year ago about Microsoft's practices in the browser market.
Firefox is IE's nearest rival in Europe, according to market share data from French researcher XiTiMonitor.
Last November IE's usage share in Europe stood at 59.5 percent, Firefox 31.1 percent, Opera 5.1 percent, Safari (Apple's browser) 2.5 percent, and Google's recently launched Chrome browser at 1.1 percent, XiTiMonitor said.
Google and Apple weren't immediately available to comment on whether they too would apply to join the EC's antitrust case.
The EC's browser case follows a landmark antitrust ruling against Microsoft in 2004, resulting in fines of over $1bn. Part of that case dealt with the bundling, or tying, of Media Player to the Windows OS.
Besides fining Microsoft, the EC also ordered the company to offer a second version of Windows with Media Player stripped out.
The second version bombed in the shops as it was sold for the same price as the bundled version.
Jon von Tetzchner, Opera's chief executive said last month he hopes the EC won't apply the same remedy in the browser case.
"The only way to give users a genuine choice is to strip out IE from Windows and either replace it with a rival browser or offer users a list of browsers to choose from," he said.
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