According to the german tech-site heise.de, the Mozilla Foundation is suing Microsoft over the use of tabbed browsing in Internet Explorer 7.
The Mozilla Foundation owns the patent 5,160,296 through one of their developers (Solomon Katz, a former Opera dev) and has begun suing Microsoft in Mountainview, California. The Foundation wants that MS immediately ceases to distribute IE 7 and pays 1.4 Billion dollars in damages. Heise reports that Microsoft has issued no official response, but is contemplating to ship IE 7 NT (no tabs).