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Firefox 3.6 likely the last for PowerPC Macs

The difficulties of supporting some new architectural features on old chips mean Firefox 4 probably will work only on Intel-basd Mac computers.

The current version of Firefox will likely be the end of the road for people using PowerPC Macs.

A final decision will be based on usage data that's better than what Mozilla possesses right now, but technical difficulties raised by Firefox 4 improvements mean at a minimum that it's a strong possibility only Intel-based Macs will be able to run the new browser.

"I am gathering data on the number of PPC users we have, but the likely outcome is that we will not be supporting PPC [PowerPC] for Firefox 4," said Mike Beltzner, Mozilla's director of Firefox, in a mailing list posting on Tuesday.

Major changes are a fact of life in the computing industry, but it's never easy to decide when users of older technology should no longer be supported. Keeping new software compatible with old hardware--and conversely, making sure new hardware can run old software--can be an expensive proposition when there are few users of the older technology left.

But Mozilla's Firefox now is used by hundreds of millions of people, and even a small fraction of them can be a large number in absolute terms. It's a plight of widely used software; for comparison, Microsoft has extended the lifespan of Windows XP several times beyond its original plans.

Dropping support for older machines, of course, can make those with the machines angry. Mozilla faced disgruntlement when it decided to cut off Firefox support for Mac OS X 10.4 after version 3.6. Using an old browser also exposes people to security risks, though Mozilla maintains older Firefox incarnations for a time after new versions supplant them.

The writing has been on the wall for PowerPC Macs for more than five years. Apple announced in June 2005 it would move to Intel processors instead of the PowerPC models built by IBM and Motorola. The two processor families use different instruction sets, so programs written for one don't run on the other without significant work.

Why phase out support?
Beltzner pointed to two new features that make Firefox 4 on PowerPC difficult. First is out-of-process plug-ins, which moves software such as Adobe Systems' Flash Player to a separate memory region to protect the main browser from crashes. This feature arrived in Firefox 3.6 for Windows, but for Macs is coming with Firefox 4.

Second is the just-in-time compiler for Web-based JavaScript programs. Faster JavaScript is a key area in the browser market competition right now, since it speeds up many complex Web sites and helps Web developers build more complicated user interfaces. Firefox is pulling in technology used in Google's Chrome and Apple's Safari, rival browsers based on the WebKit browser project, to help speed JavaScript.

"I believe that Firefox 4 should be relatively faster and superior to previous versions--so to be better than Firefox 3.6. Two of the significant mechanisms for performance improvement will not be available for PPC based computers, and so we are not planning on extending Firefox 4 support to those architectures," Beltzner said in another mailing list message.

It's possible a version of Firefox for PowerPC could be built without those features, he added--but it probably wouldn't be called "Firefox." "I suspect that we won't brand any of those builds as 'Firefox' though, but that would be a discussion with whomever wishes to publish those builds, as usual," he said. "Our goal is to deliver a consistent Firefox experience across platforms."

Beta schedule slip
Plans are changing for building the next test versions of Firefox.

Mozilla released Firefox 4 beta 4 Tuesday and had hoped to "freeze" the code base for beta 5 this Friday, a step that locks most development out as a new version of the software is built. This fifth beta had been planned as a significant milestone: the first test version to have all the Firefox 4 features built in, if not fully tested.

However, Mozilla is having trouble meeting that goal.

In meeting notes published Tuesday, Belzner proposed making the sixth beta the last to get new features. The target date for the beta 6 code freeze is September 10.

Mozilla is assessing the priorities for that release. Priorities include performance, a better user interface that could help attract people to upgrade, and the new Jetpack extensions framework that could make it easier to upgrade Firefox without forcing add-on programmers to rebuild their software.

And one important Web technology development looks like it won't be ready in time for Firefox 4: IndexedDB, which builds database abilities into the browser so that Web applications can work offline, among other things. "IndexedDB unlikely to be included (spec is changing rapidly, security implications to be resolved," Mozilla said in notes for a weekly meeting.

Another development, the WebSocket interface, is "likely to be included, but only as...experimental," the planning notes said. The WebSocket interface opens up a communication channel between the browser and a server, making it easier to build a Web site or application that's continuously updated.