Mozilla has officially announced the release of Firefox 9, although savvy users have been able to download Firefox 9 labelled builds since earlier this morning.

The big improvement in this release is that Firefox’s SpiderMonkey JavaScript engine now has type inference that allows the engine to conduct code analysis and monitoring of values during execution, which in turn allows the JaegerMonkey JIT compiler to generate more efficient code. The result is up to 30 per cent improvement in JavaScript execution times.

Credit: Mozilla

“Javascript is a dynamically typed language, and without knowing the types of values a JIT compiler needs to generate code that accounts for all the possible types of the involved values. This significantly slows down execution of the program in comparison with a statically typed language like Java. With TI integration into JaegerMonkey, we are closing a significant part of this performance gap” wrote Brian Hackett, Firefox engineer, in a blog post when type inference hit Firefox’s Beta channel.

Other improvements for developers include the ability to provide start and stop times for <audio> and <video> elements, support for chunking of AJAX requests which allows content display as it is downloaded, rather than waiting for a complete download, and allowing Firefox on Android users to take photos with their phone’s camera without leaving the browser for input elements used with type=”file” and accept=”image/*”.

A list of changes for developers can be found here.