For the second time in the past four weeks, Mozilla Corp. has announced a "code freeze" for a beta version of Firefox 3.0 – this time, Beta 4 – as it prepares another public release of the open-source browser.

The freeze was announced late Tuesday. Earlier in the day, the company's chief engineer hinted that the number of outstanding bugs at that point – 66 that could block the release of Firefox 3.0 – meant a fifth beta will probably be needed.

"We reviewed the remaining number of P1 [Priority 1] and P2 [Priority 2] blockers on our lists and decided that we would go ahead with tonight's Firefox 3 Beta 4 code freeze and then bake nightly builds for a few days before handing off the code to the build and quality assurance teams," said Mike Beltzner, Mozilla's interface designer, in a message posted to the company's developer center.

During the rest of the week, Beltzner continued, developers will be looking over the blocking bugs to decide which, if any, require another beta release and which would prevent the final release of Firefox 3.0 if they went unfixed.

Meanwhile, Mike Schroepfer, the company's vice president of engineering, said he is leaning toward a fifth beta to give developers a chance to quash potential blockers. "As of this writing, there are 66 P1 bugs, which implies we either will not meet code freeze tonight or will need to add another milestone," he said hours before Mozilla held its weekly status meeting on Firefox 3.0. "Given the number of improvements between Beta 3 and today's nightly, I'd strong prefer we meet the freeze and talk about doing an additional Beta."

However, Schroepfer also pushed for releasing Firefox 3.0 soon. "Given the amazing positive feedback and the fact that we have [500,000] daily active users of Firefox 3 (with basically hockey-stick growth of usage) I think we should push to final as fast as possible," he wrote in a message posted to the mozilla.dev planning newsgroup early yesterday.

Previously, Schroepfer had refused to specify a release date for the final version of Firefox 3.0, although he had pointed to early March as the goal for Beta 4. Another beta would push out final delivery of a finished Firefox by approximately four weeks, based on the last interval between previews.

Mozilla froze Firefox 3.0 at Beta 3 on Jan. 29, and released that build two weeks later, on Feb. 12.

Firefox currently accounts for about 17% of the browser usage share, according to Net Applications Inc., an Aliso Viejo, Calif.-based Web measurement company. The most recent data available, for January, pegged Firefox 3.0's part of the browser market at just 0.1%, in comparison with Firefox 2.0's 16.02%.