A menu item (File->Save As), which is a part of Wang's patent from 1984 on "Video Text Systems". At 1999, they've (a Microsoft-ally at that point) has claimed Netscape's infringment of the patent in Netscape Navigator software. At the same opportunity, Netscape was also sued for the Bookmarks concept and Saving files with file extensions and then retrieving the pages and decoding the files based on the file extension. The lawsuit was later dismissed, as the court found that patents, which were filled for Teletext systems, didn't apply to computers.

Read more at http://www.mozilla.org/legal/wangsuit.html