Mozilla decided Tuesday to roll out a second release candidate for Firefox 3.0 that will include fixes for about 40 bugs. The alternative was to declare the open-source browser good "as is," then patch the problems with a later update.

Firefox 3.0's final release will be delayed about five days, according to notes from a Tuesday meeting that Mozilla posted to its site.

"As discussed at today's Firefox 3.0 meeting, we've decided that there is sufficient need to produce a new Release Candidate before shipping," said Mike Beltzner, Mozilla's lead developer, in an e-mail. "Due to the time required to complete some other external dependencies, we don't expect that this will significantly impact our shipping date, and still estimate a mid-June release date."

Release Candidate 2 (RC2) will be closed as "code complete" Wednesday, a tight timetable possible only because most of the issues uncovered by testers in the first release candidate have already been patched, reviewed and approved. "Because of the early start we got last week identifying the bugs that would be part of an RC2, which, at that time, was speculative, we're in really good shape," added Beltzner.

Only three of approximately 40 identified bugs have not yet "landed," or completed Mozilla's review and approval process. About a fourth of the bugs Mozilla's planning to patch in RC2 are changes in localized versions of the browser.

Last week, Mozilla highlighted 10 notable bugs that it said it would consider as it made a choice between RC2 and a later update, dubbed "3.0.1", that would be released several weeks after Firefox 3.0 shipped.

One of those bugs, a performance issue limited to Linux, got attention this morning before the RC2 go/no go meeting. "This was discussed at the [last] Tuesday meeting and is a decent perf[ormance] win if we can get this in," read the early notes. "It tends to make the UI unusable when the user hits this state, so it should be considered for an RC2."

The Linux bug got attention in part because of a blog post by Jason Clinton, who works for Advanced Clustering Technologies Inc., a Kansas City, Kan., company that specializes in cluster-based systems and Linux servers. A week ago, Clinton took Mozilla to task over its then-reaction to the bug, which he said showed the company's "second-class" support for the open-source operating system.

Friday, however, after developers had gone back and forth on Bugzilla, Mozilla's bug-tracking database and management system, and come up with two possible solutions, Clinton changed his tune. "Mozilla really stepped up and has demonstrated that they do consider Linux a first-class platform," he wrote in a follow-up post.

If Mozilla adheres to its posted schedule, it will release Firefox 3.0 RC2 sometime after June 5. Previously, Mozilla has said it requires at least a week between debuting a release candidate and -- assuming no major problems crop up -- calling that build final.

Firefox 3.0 will be the first major upgrade to the browser since October 2006, but perhaps not the only one this year. Mozilla's head of engineering last week said that Mozilla may ship another upgrade, tentatively labeled Firefox 3.1, before the end of the year in order to add features that didn't make it into Firefox 3.0. Among the pieces which weren't ready in time for 3.0 but would be for 3.1, Mozilla has cited support for Cross-site XMLHttpRequest, a specification that lets a Web page draw information from servers behind firewalls, and additional performance tuning.