More than 7 million users downloaded Mozilla Corp.'s Firefox 3.0 Web browser during the first 24 hours after its launch, according to the company. A Web metrics company tracking hour-by-hour use of Firefox 3.0 added that the new version quadrupled its market share during the first day. Although Mozilla's download servers were offline for more than an hour Tuesday after the scheduled 1:00 p.m. Eastern launch, 8.3 million copies of the browser were downloaded in the first 24 hours, Mozilla's