To take advantage of the speed benefits of TraceMonkey, JägerMonkey compiles complete methods as machine code in such situations, even if this process is a bit slower. In return, the compiled code can be used much more often. If this strategy can be effectively implemented, Firefox could take over the competition and be back at the head of the pack.
As recent benchmarks by Mozilla developer Rob Sayre show, Mozilla may have sped up remarkably thanks to this approach by the time Firefox 4 has been released. While Internet Explorer 9 Preview 3, Webkit in the developer version from September 08, 2010, Chrome 6.0.472.55 and Opera 10.61 are all faster, the gap has shrunk considerably.
Nightly preview builds of Firefox JS running JägerMonkey are available to download from the project's site. As with all development releases, use in production environments and on mission critical systems is not advised.
- Jägermonkey: it’s in ur browser!!!, a Mozilla blog post.