The Mozilla Foundation has released a second beta of the Firefox 1.5 Web browser that, like the first version released last month, focuses on tackling nagging security issues.

Beta 2 became available on Friday for download. The release comes just a month after Beta 1 of the browser became available publicly. Version 1.5 is Firefox's first major update since the browser officially debuted last year.

Mozilla noted on its Web site that the latest beta "does not contain any major new features since Beta 1. Improvements to automated updated system, Web site rendering and performance, along with several security fixes, are included in this release."

Although Microsoft's Internet Explorer Web browser has in the past received more criticism for security holes than Firefox, the latter browser has also come under fire. In its semiannual report about Internet security threats, IT security vendor Symantec said last month that Firefox had more confirmed vulnerabilities in the first six months of the year than did Internet Explorer.

Symantec said that doesn't necessarily mean that Firefox is less secure than proponents have claimed or that Internet Explorer is safer than many users believe.

Firefox has quickly become a challenger to the dominance of Internet Explorer. According to July data from NetApplications.com, a monitor of Web site usage, Firefox was used by 8.1 percent, while Internet Explorer was used by 87.2 percent. Apple Computer's Safari, available only for Mac OS X, had 2.1 percent of users. But Firefox's market share actually fell more than half a percentage point from April, according to NetApplications.

Meanwhile, WebSideStory reported last month that Firefox's market share grew just a single percentage point in five months, to 7.9 percent at the beginning of September.

Mozilla officials said at Firefox's launch last October that they expected to garner 10 percent of the market by the end of 2005.

The final release of Firefox 1.5 is expected by year's end.

Microsoft, meanwhile, is now testing the first beta of its updated Internet Explorer 7 with Web developers. Internet Explorer 7 promises improved security against viruses and spyware, including protection against so-called phishing attacks designed to steal users' personal data. It also replicates popular usability features in Firefox such as tabbed browsing.

Microsoft is expected to release the final version of IE 7 to the public by next spring.