ActiveState Community

That is the source code to the casper extension. To create the extension you'll need to package the code into an xpi file. You can easily accomplish this by using the Komodo sdk:

$ svn co http://svn.openkomodo.com/openkomodo/browse/openkomodo/trunk/src/modules... casper
$ cd casper
$ <komodo_install_dir>/lib/sdk/bin/koext build

which will create something like "casper-1.0-ko.xpi", which should then be installable into Komodo, Firefox, Thunderbird, etc...

Note: If your not using Komodo, you can still package the extension using standard zip tools, there are Mozilla docs covering extension packaging.