Mozilla has renamed the oft-delayed Firefox 3.1 to Firefox 3.5 and said a fourth beta of the browser is slated for a 14 April release.

A possible name change has been batted around inside Mozilla Towers for several weeks, but the outfit finally confirmed the decision yesterday.

“As recently proposed, the version number of the Shiretoko project will be changed to Firefox 3.5 before the upcoming fourth beta release,” said Firefox director Mike Beltzner on the corporation's developer blog.

The number of new features that have been packed into the upcoming version of Internet Explorer’s closest rival meant it was necessary to reflect those changes in the name, said Mozilla’s engineering veep Mike Shaver last week.

"The increase in scope represented by TraceMonkey and Private Browsing, plus the sheer volume of work that's gone into everything from video and layout to places and the plugin service make it a larger increment than we believe is reasonable to label 3.1," he said.

Mozilla posted a proposed timeline for its developers to move various systems from Firefox 3.1 to Firefox 3.5 on the corporation’s wiki yesterday.

It details the planned changes to the release, which has already been hit by several delays due to show-stopping bugs.

In January Mozilla was unable to confirm when it would release the third beta of Firefox 3.1 after 15 nasty bugs were discovered in TraceMonkey, which is the firm’s new JavaScript Engine. Beta 3 is expected to land this Thursday and will be the final Firefox release to carry the 3.1 tag.

“It’s important to note that 3.5 represents a better labeling of our current scope, and not an indication that we intend to significantly increase this release’s scope any further,” said Shaver.

But the version switcheroo could ruffle feathers among the wider developer community, where some have grumbled about the number of delays the corporation has already hit with its upcoming browser release.

Last summer it was a slightly different story when Mozilla's platform evangelist Mark Finkle insisted on his blog that the transition to Firefox 3.1 wouldn’t be “a major pain-in-the-ass”, and pledged developers wouldn't be hit by “surprises along the way”. ®