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21 December 2011, 09:21

Firefox 9 improves JavaScript performance

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As expected, the Mozilla Project has now officially released version 9.0 of its open source Firefox web browser. Based on the Gecko 9.0 rendering engine, Firefox 9.0 brings under the hood changes that improve JavaScript performance by up to 30 per cent; early tests by ExtremeTech confirmed Mozilla's estimates, but found that it could also occasionally be slower.

Type inference, a new feature in this release, provides the browser's just-in-time compiler (JIT) with reliable information on variable types. This enables it to generate more efficient code which does away with many of the runtime checks which were previously required because variables in JavaScript are dynamically typed (i.e. the data type is not necessarily determined at compilation time).

Zoom JavaScript in version 9 is up to 30 per cent faster than Firefox 8
Source: Mozilla
The algorithm developed by Mozilla's programmers is described in detail in Fast and Precise Hybrid Type Inference for JavaScriptPDF. It uses conventional static code analysis as its starting point, but adds in dynamic aspects using "type barriers", at which the JIT compiler checks a variable's current type and modifies the generated code where appropriate.

On Mac OS X 10.7 Lion, Firefox 9 now supports two finger forward and backward navigation. Support for the text-overflow and font-stretch CSS3 properties has been improved, and it is now possible to determine the "Do Not Track" setting via JavaScript. Standards compliance for HTML5, MathML and CSS has also been enhanced.

More details about this update, including a list of bug fixes, can be found in the release notes and on the Firefox 9 for developers page. Firefox 9.0 is available to download for Windows, Mac OS X and Linux. Existing users should receive an automated update notification; alternatively, users can manually check for the update.

Firefox binaries are released under the Mozilla Firefox End-User Software License Agreement and the source code is released under disjunctive tri-licensing that includes the Mozilla Public License, GPLv2 and LGPLv2.1.

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