Mozilla has decided that when it comes to Android devices, performance is more important than the wealth of add-ons that can be used to customize Firefox.

Yesterday, Mozilla Director of Firefox Engineering Johnathan Nightingale announced on a mailing list that Firefox will move to Android's native user interface, ditching the XUL technology that's been in use by Mozilla since before there even was a Firefox.

"Firefox on Android is a critical part of supporting the open Web, and this decision puts us in a position to build the best Firefox possible," Nightingale said.

Firefox is widely used on personal computers but a rarity on mobile phones, where--unlike Apple's Safari or the unbranded browser Google builds for Android--it's not installed on any phones by default. Firefox is the chief way Mozilla tries to implement its vision of empowering users of the Web and keeping that Web an open technology.

Firefox with a native Android interface should mean faster start-up, less memory usage, and smoother zooming and panning, Nightingale said. The native UI project page for mobile Firefox, aka Fennec, also listed better battery life as a benefit.

It's not clear when the rebuilt version will arrive, but it won't be for either the beta or Aurora versions currently in testing, Nightingale said.

Start-up time is a big deal when comparing Firefox with the built-in browser on Android, especially since Firefox often gets kicked out of memory when not in use, forcing another sluggish load when a person taps a link and needs the browser again.

"After substantial discussion, we have decided to build future versions of Firefox on Android with a native UI [user interface] instead of the current XUL implementation," Nightingale said.

Only the user interface will change; the browser will still use the underlying Gecko engine for processing Web page elements. But leaving XUL behind will be a big deal for anyone who built Firefox add-ons using the technology, and it complicates the process of translating Firefox into different languages, too.

"It's still early days, so we have a lot of questions to answer," Nightingale said. "We're talking with the Add-on SDK team about the best way to support extensions. We're talking with l10n [localization] about how to ensure we support Firefox users wherever they live around the world."

One possibility, according to some meeting notes on native-UI Firefox, is blunter: "Extensions are gone." The notes raise the possibility of using Mozilla's Add-On Software Developer Kit (SDK), an online tool for creating add-ons, but at present that works only for new-style "Jetpack" add-ons that aren't available on mobile right now.

For now, there's a lot of planning to do in regard to the transition.

"By the end of next week, we will have a clearer outline of the work ahead," Nightingale said.