Turns out the current top-answer by @sunsean does not work as expected when it comes to handling multiple loads. The function should properly close over the document and avoid global state.
Also, you have to call jQuery.noConflict(true)
to really avoid conflicts with other add-ons!
This is who I would write it (then again, I would avoid jquery (in add-ons) like the plague...).
First the overlay XUL
<?xml version="1.0"?>
<overlay id="test-addon-overlay" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
<script type="text/javascript" src="jquery.js"/>
<script type="text/javascript" src="overlay.js"/>
</overlay>
And then the overlay script:
// Use strict mode in particular to avoid implicitly var declarations
(function() {
"use strict";
// Main runner function for each content window.
// Similar to SDK page-mod, but without the security boundaries.
function run(window, document) {
// jquery setup. per https://stackoverflow.com/a/496970/484441
$ = function(selector,context) {
return new jq.fn.init(selector,context || document);
};
$.fn = $.prototype = jq.fn;
if (document.getElementById("my-example-addon-container")) {
return;
}
let main = $('<div id="my-example-addon-container">');
main.appendTo(document.body).text('Example Loaded!');
main.click(function() { //<--- added this function
main.text(document.location.href);
});
main.css({
background:'#FFF',color:'#000',position:'absolute',top:0,left:0,padding:8
});
};
const log = Components.utils.reportError.bind(Components.utils);
// Do not conflict with other add-ons using jquery.
const jq = jQuery.noConflict(true);
gBrowser.addEventListener("DOMContentLoaded", function load(evt) {
try {
// Call run with this == window ;)
let doc = evt.target.ownerDocument || evt.target;
if (!doc.location.href.startsWith("http")) {
// Do not even attempt to interact with non-http(s)? sites.
return;
}
run.call(doc.defaultView, doc.defaultView, doc);
}
catch (ex) {
log(ex);
}
}, true);
})();
Here is a complete add-on as a gist. Just drop in a copy of jquery and it should be good to go.