By Gregg Keizer
June 29, 2009 01:08 PM ET

Mozilla will ship Firefox 3.5 on Tuesday, bringing the long-awaited upgrade in under its own deadline wire, the company announced last Friday. According to a Mozilla spokeswoman, the final version of Firefox 3.5 will be posted for download tomorrow morning, Pacific time.

The news was not a surprise. Last Thursday, Mike Beltzner, the director of Firefox strongly hinted that Firefox 3.5 would meet the ship deadline of the first half of the year. "Everyone's pretty happy with the release, and while we haven't picked a date yet, we're still tracking to our latest schedule," Beltzner said in an e-mail. Mozilla made its deadline by running an unusual, accelerated set of release candidates (RC) that were issued primarily to the 800,000 users running earlier previews of the new browser.

In early June, it pushed an interim "Preview" build it described as a nearly-finished RC and last week it wrapped up the process with several quick RCs. The release comes just over a year after Firefox 3.0 debuted. Firefox 3.5 was originally slated to be called Firefox 3.1, but the company decided in March that it had added enough new features to justify the larger bump in number from last summer's Firefox 3.0.

Among the features to debut in Firefox 3.5 are a new, faster JavaScript engine called TraceMonkey; a privacy mode, which some call "porn mode" for one of its more obvious applications; and location-aware browsing. Mozilla has also touted numerous under-the-hood performance improvements, ranging from support for new video and audio HTML5 tags to support for Web worker threads -- enhanced scripting that lets site developers shift JavaScript computations to a background thread.