As it happens, making sure the Open Komodo codebase works on XULRunner and runs on trunk is a big aim of the Komodo team as well! We're really looking forward to getting other people into the code, if you have any questions please let us know.

If you want to poke around in the code right now, probably the best thing to do is grab Komodo Edit[1] and check out the ko.* JS API[2], as well as our IDLS[3]. Writing macros and extensions on Komodo can be a great way to dig into the API without having to do a full build environment.

[1] http://downloads.activestate.com/Komodo/

[2] The ko.* namespace documentation is included in Komodo's Help docs.

[3] From Komodo 4.1 and on, the IDL files can now be found in the Komodo install directory:
<install_dir>/lib/sdk/idl