Firefox 18 Beta wields an IonMonkey for JavaScript

Mozilla is aiming to deliver faster JavaScript in the new beta version of Firefox 18 by incorporating the IonMonkey just-in-time compiler as a replacement for the SpiderMonkey JavaScript engine. IonMonkey was introduced with the alpha of Firefox 18 in September and is designed to improve the performance of long running JavaScript applications; short-running applications will still be run using the JägerMonkey engine. When IonMonkey was introduced, Mozilla's David Anderson noted improved performance over past Firefox and Chrome releases on a number of benchmarks.

The Firefox 18 beta is not just about an improved JavaScript engine though. The release notes note that it now supports Apple's Retina Displays on Mac OS X 10.7 and up and it includes initial support for WebRTC, the audio and video real time communications protocol which enables a range of new web applications with real time chat.

Changes in the beta include better image quality as the developers have changed the algorithm used when scaling HTML imagery, and switching between tabs should be somewhat faster thanks to some performance tweaks. Developers will find that CSS3's Flexible Boxes have now been implemented to allow for a simpler, more responsive style of layout of page elements, window.devicePixelRatio will now give the ratio between physical pixels and device independent pixels on a display and @supports is now available to conditionally apply code when a feature is (or isn't) supported. There are also improved startup times and support of the W3C touch events is now implemented, in place of the MozTouch events.

Fixes in the beta include the disabling of insecure content loading on HTTPS pages, a bug that has been in the Mozilla bug system since 2000. For now, the feature requires enabling though through about:config. There is also, according to the notes, better responsiveness for users working through proxies. Issues still present include Firefox crashing if starting with a locked profile, slow scrolling on gmail, issues with Microsoft's System Restore and a problem with reporting with the -private flag.

Firefox 18 Beta is available from the Firefox Beta channel and is licensed under the Mozilla Public License 2.0.

(djwm)