Does it feel like you just updated to Firefox 8? That is because you literally did just update to Firefox 8. But hey, Mozilla has a rapid release cycle schedule to meet. Who cares if these rapid updates are bloody annoying. Here comes Firefox 9.

Firefox 9 doesn’t contain as many user-facing changes as previous updates. Rather, most of FF9 changes are under-the-hood, aiming to make up for Firefox’s recently bloated past:

• Added Type Inference, significantly improving JavaScript performance
• Improved theme integration for Mac OS X Lion
• Added two finger swipe navigation for Mac OS X Lion
• Added support for querying Do Not Track status via JavaScript
• Added support for font-stretch
• Improved support for text-overflow
• Improved standards support for HTML5, MathML, and CSS
• Fixed several stability issues

The biggest change in FF9 is undoubtedly the new Type Inference:

Firefox 9 features the release of Type Inference, or TI, a research project under way for over a year. TI is a feature in the SpiderMonkey Javascript engine which generates type information about Javascript programs through a combination of analyzing the program’s code and monitoring the types of values as the program executes. This type information is used during JIT compilation to generate more efficient code; Firefox 9 includes modifications to the JaegerMonkey JIT compiler to use inferred type information. This compilation mode, which is the default in Firefox 9, speeds up major benchmarks like Kraken and V8 by over 30%, and gives a large speed boost to many JS heavy websites.

Now that we know why Mozilla insisted on releasing Firefox 9, let’s hope we don’t break anything (particularly add-ons) while upgrading.

Firefox 9 is going to be rolled out through Firefox’s auto-update starting December 20, 2011. If you are impatient, you can manually update by downloading FF9 from Mozilla’s FTP repository.

Official Mozilla Firefox 9 FTP Repository

[via Ghacks]