sending a message from a CI application to a content script

CI doesn't "talk" to client-side scripts, but it can respond to AJAX requests from them.
There could be an addin that integrated the two more along the lines of what you are looking for.

I already have a background script that "talks" to a CI daemon. But I am looking to go the other way, from the CI app (in the browser) to the background script. The background script could "poll" the CI app to see if the user logged on to the CI app. But I really think this is wasteful since 99% of the Extension users won't be running the the CI app. I think I need to go from the CI display (perhaps by injecting a frame?) in the browser to the content script.

proof that an old dog can learn new tricks