Mozilla has released Firefox 3.5, ending six months of delays to complete the browser almost exactly a year after its last major upgrade.

"There are some great new enhancements here," said Sherri McLeish, an analyst with Forrester Research, who noted that some of those additions are playing catch-up to Internet Explorer 8 and Google Chrome. "Part of this release is to provide a private browsing mode," she told Computerworld US.

Firefox logo The release of Firefox 3.5 means the clock is ticking for Firefox 3.0. Mozilla's policy is to support an older edition for only six months after the launch of a successor, meaning the company is likely to stop producing security patches for Firefox 3.0 on December 31, 2009.

Current Firefox 3.x users can update now by selecting ‘Check for Updates' under the ‘Help' menu.

McLeish said Mozilla had an opportunity to increase Firefox's market share in Europe in light of Microsoft's decision to strip Internet Explorer 8 from Windows 7.

Microsoft announced the move, seen as an effort to steer clear of further antitrust woes, last month.

"Open-source is certainly well-received in the EU," said McLeish, "but [any change in share] will really depend on what decisions the OEMs make, and how they will offer alternative browsers. It's too early to get any insight into what those relationships will be. But it's a good time for Firefox or Chrome, or even Opera, to forge new relationships with OEMs."

Mozilla Firefox 3.5 review