Wow, this is useful. I have run into the same situation, but never pursued a solution. Thanks for sharing.

I'm using the following technique for quite some time now:
To generate the event in the webpage:

top.mydata = mydata //can be any object
var event = document.createEvent("Events");
event.initEvent("myevent", true, true);
top.dispatchEvent(event);

To catch the event in chrome:

addEventListener("myevent",onMyEvent,false,true);
function onMyEvent(event) {
var target = event.target.wrappedJSObject;
var mydata = target.mydata;
//....
}

No need for a component

(From Alex: Due to an ancient architectural bug in our software, we couldn't do that. top.mydata would only allow one slot worth of data to be carried; it's not OOP. The solution I came up with is more flexible. On top of that, events are a little expensive on the Mozilla code - there's a lot of nodes which have to process the event, even if only to detect whether the event affects them or not.)

Yeah - this could be really useful. I've needed something like this for a while, but wasn't sure it was possible, so I didn't spend a lot of time trying to figure it out. As a general capability, it could really open up the possibilities for cool extensions that do things with web pages. Firefox really needs something like that to really take off.

what a beautiful man you are :)
I had given up being able to send message from content to chrome. I basically had to create a div with a certain ID and on each page load my extension would watch for that id, then assign a certain onclick I needed for it.

For people who find this page -and- read the comments, here's the solution I've been recommending for people to use:

http://forums.mozillazine.org/viewtopic.php?p=1005555#1005555

Note that it's slightly different from the solution in comment 2 - it doesn't use wrappedJSObject, so it is generally safer. If you want to pass more complicated structures than just strings, you can pass the JSON representation of those structures.