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.
From Firefox 53 onwards, no new legacy add-ons will be accepted on addons.mozilla.org (AMO).
From Firefox 57 onwards, WebExtensions will be the only supported extension type, and Firefox will not load other types.
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 WebExtensions if they can. See the "Compatibility Milestones" document for more.
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.
To list the open tabs, you can iterate over the tabs object itself.
The following add-on adds an action button that logs the URLs of open tabs when the user clicks it:
require("sdk/ui/button/action").ActionButton({
id: "list-tabs",
label: "List Tabs",
icon: "./icon-16.png",
onClick: listTabs
});
function listTabs() {
var tabs = require("sdk/tabs");
for (let tab of tabs)
console.log(tab.url);
}
Note: to get this working, you will need to save an icon for the button to your add-on's "data" directory as "icon-16.png". You can download the icon here: 
.
Run the add-on, load a couple of tabs and click the button. You'll see output in the command line console that looks something like this:
info: http://www.mozilla.org/en-US/about/ info: http://www.bbc.co.uk/
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/ui/button/action").ActionButton({
id: "list-tabs",
label: "List Tabs",
icon: "./icon-16.png",
onClick: listTabs
});
function listTabs() {
var tabs = require("sdk/tabs");
for (let tab of tabs)
runScript(tab);
}
function runScript(tab) {
tab.attach({
contentScript: "document.body.style.border = '5px solid red';"
});
}
Learning More
To learn more about working with tabs in the SDK, see the tabs API reference.
To learn more about running scripts in tabs, see the tutorial on using tab.attach().