Nobody will seem strange to read that sometimes Firefox is slower than other browsers (compared for example with Google Chrome). The slowness of Firefox can be seen in several parameters, one of them is for example the JavaScript engine, which is responsible for recognizing and interpreting the JS code is in web pages.

This is a very important part of the browser, and is used as parameter when doing benchmarks (performance tests).
Today Firefox is behind Chrome, Opera and Safari in performance when doing basic tasks with JavaScript code.

The Mozilla browser has nanojit as motor (in fact this project was developed by Adobe to interpret ActionScript in Flash. It is also open source since 2006), which has a regular performance.

The new engine called JägerMonkey, will nanojit parts, however their main base and more solid will be formed with pieces of code from Apple Webkit project in an attempt to make Firefox more about their competitors, especially when running JavaScript code.

This new heart for Firefox is at a very early stage of development and still not be distributed widely. For developers, there is a place where you can download the source code and also check the status of the project.

Link Starting JagerMonkey
Via ArsTechnica