The Venkman JavaScript debugger extension works perfectly in Conkeror. After installing it, you can start it in one of two ways. From the command line:

conkeror -batch -venkman

Or, after enabling a glue-code module that comes with Conkeror, from a M-x prompt. To enable the glue-code module, put the following in your rc:

require("venkman");

Then you can start Venkman with M-x venkman.