Mozilla today shipped Firefox 4 Beta 9, perhaps the last it will release before it pushes toward a final version now planned to ship by the end of February.

The newest beta includes fewer major changes than its December 22 predecessor, with just a pair of performance improvements including one to the code that handles the browser's bookmarks and history list, called out by Mozilla.

According to Mozilla, Beta 9 sports 662 bug fixes or changes, less than half of the 1,400 it made in Beta 8, which launched a little over three weeks ago.

Although Mozilla picked up the pace between Beta 8 and 9 the company is pushing developers to get the code in shape for a "release candidate," the last major milestone before the browser is deemed good enough to officially ship.

Hard blockers

Earlier this week, Mozilla's head of platform engineering said there were still too many "hard blocker" bugs, flaws that would prevent Firefox 4 from final release, and urged developers to "press hard" toward a February finish line.

In a follow-up blog post Thursday, Johnathan Nightingale, the director of Firefox development, called on all programmers to reevaluate their blocking bugs. Saying that developers must take a "hard look at our blocker list," Nightingale added that, "at this point, very few bugs are worth holding back that much awesome."

Nightingale said that as of Thursday, 143 hard blocker bugs remained, and detailed which flaws fit into the category. "A hard blocker is a failure of a core part of our release criteria, e.g. a crash, a memory leak, a performance hit, a security issue, a [user interface] breakage that can't be recovered from, an incompatibility we can't stomach," he said.

It's currently unclear if Mozilla will do a 10th beta.

Although Firefox Beta 10 remains on a still-current schedule that shows on Mozilla's website, on Monday Damon Sicore, who leads the company's engineering group, hinted that Beta 9 might be the last. "If we can't get [bugs] to zero in reasonable time, we'll repeat [a tenth beta]," he said on a Firefox developers mailing list.

By Mozilla's schedule, Beta 9 was nearly a month late.

Firefor 4 Beta 9 can be downloaded for Windows, Mac OS X and Linux from Mozilla's site.