The problem is that if your extension includes a binary XPCOM component that uses unfrozen interfaces (and it is hard not to, lots of things are unfrozen), then it is highly likely that you will have to recompile your component for each new version of the Gecko SDK (and therefore most new major versions of Fierfox).
The Mozilla wiki proposed the idea of using a "stub component" to sniff the environment version and load the right XPCOM component, but this is pretty complex to implement.
I realized that you can just use JavaScript to do the same, and it is trivial. Hope this helps someone else out (I've also updated the wiki).
