Listen for Page Load


Support for extensions using XUL/XPCOM or the Add-on SDK was removed in Firefox 57, released November 2017. As there is no supported version of Firefox enabling these technologies, this page will be removed by December 2020.

Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.

Starting from Firefox 53, no new legacy add-ons will be accepted on (AMO) for desktop Firefox and Firefox for Android.

Starting from Firefox 57, only extensions developed using WebExtensions APIs will be supported on Desktop Firefox and Firefox for Android.

Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to use WebExtensions APIs if they can. See the "Compatibility Milestones" document for more information.

A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.


To follow this tutorial you'll need to have learned the basics of jpm.

You can get notifications about new pages loading using the tabs module. The following add-on listens to the tab's built-in ready event and just logs the URL of each tab as the user loads it:

require("sdk/tabs").on("ready", logURL);
function logURL(tab) {

You will find this console output in the Browser Console, not the Web Console.

You don't get direct access to any content hosted in the tab.

To access tab content you need to attach a script to the tab using tab.attach(). This add-on attaches a script to all open tabs. The script adds a red border to the tab's document:

require("sdk/tabs").on("ready", runScript);
function runScript(tab) {
    contentScript: "if (document.body) = '5px solid red';"

(This example is only to show the idea: to implement something like this, you should instead use page-mod, and specify "*" as the match-pattern.)

Learning More

To learn more about working with tabs in the SDK, see the tabs API reference. You can listen for a number of other tab events, including open, close, and activate.

To learn more about running scripts in tabs, see the tutorial on using tab.attach().