Gecko has built-in cross platform profiling support. This extension is designed to provide a front end to this profiling support.
For more details see: https://developer.mozilla.org/en/Performance/Profiling_with_the_Built-in_Profiler
For the platform support see 'tools/profiler' in gecko.
You can use the pre-built add-on 'geckoprofiler.xpi'. Just drag into your Firefox window.
In order to build this add-on, you need a copy of the add-on SDK. Please use the bootstrap.sh script.
Use ./run.sh and ./build.sh to exec and package the add-on.