Mozilla Corp. will unveil a release candidate of Firefox 2.0 later Tuesday, the next step toward finalizing the browser's first major upgrade in a year.

According to notes posted in the developers' section of the Mozilla Web site, Firefox 2.0 RC1 is on track to debut Tuesday, Sept. 26. "This is just to let everyone know that the QA testing for RC1 is complete," read the note.

Firefox 2.0 has already gone through a pair of beta versions; the last, Beta 2, was released at the end of August. Mozilla has not set a release date for the final.

At least one more release candidate will be posted before the final is put on the street, Mike Schroepfer, Mozilla's director of engineering, wrote elsewhere on the company's site. "We have a handful of bugs that look reasonable to cause a FF2 RC2," said Schroepfer, who also urged staff and volunteer developers to keep moving.

"We are in the end game here - which means days matter and our tolerance for risk is *zero*. We will not take bugs unless they are of great benefit: crashes, web compatibility, and major regressions. IMHO [In My Humble Opinion] FF2 RC1 is already a tremendously superior product to FF15. So let's wrap this up!"

Firefox 2.0 features several additions and improvements to 1.5, which was released in November 2005, including anti-phishing alerts, session restore, spell checking, and suggested searches. The open-source browser, which will roll out as RC1 in versions for Windows, Mac OS X, and Linux in nearly 50 localized editions, will compete later this year with Microsoft's Internet Explorer 7, which is also currently in Release Candidate form.

Firefox 2.0 RC1 can be downloaded from the Mozilla.org Web site starting at 3 p.m. PDT on Tuesday.