We are planning to deprecate the use by Firefox add-ons of the techniques described in this document. Don't write new add-ons that use these techniques.
The following items are accessible in the context of chrome://browser/content/debugger.xul (or, in version 23 beta, chrome://browser/content/devtools/debugger.xul):
- window.addEventListener("Debugger:EditorLoaded") - called when the read-only script panel loaded.
Unfortunately there is not yet any API to evaluate watches/expressions within the debugged scope, or highlight elements on the page that are referenced as variables in the debugged scope. (currently a work in progress, see bug 653545.)