The latest version of the open source Firefox Web browser recently reached the 20 million download mark, according to Mozilla. The software is also closing in on 10% of the overall market for Web browsing, industry observers say, adding that it is the first time since 2002 that a non-Microsoft Web browser approached such market share.Among the new features touted in Firefox 1.5 include better product updating notification, the ability to drag and drop browser tabs, faster performance and better pop-up blocking.While Firefox did not meet Mozilla's stated goal of reaching 10% of the browser market by the end of 2005, the open source browser didn't have a bad year, exactly. As vulnerability warnings about Microsoft Internet Explorer (IE) become almost daily news flashed in newsletters similar to this one, Firefox has so far either proven more resilient, or less of a target to hackers. (Security data tracking Web site Secunia lists the number of security advisories for IE at 91, while Firefox has accounted for 26 advisories.)A recent survey by Desktoplinux.com showed that Firefox was the most popular browser among Linux desktop users. A close second was Firefox's sibling the Mozilla browser, which Firefox code is based on.