WebExtensions for Firefox 49

Firefox 49 landed in Developer Edition this week, so we have another update on WebExtensions for you!

Since the release of Firefox 48, we feel WebExtensions are in a stable state. We recommend developers start to use the WebExtensions API for their add-on development. Since the last release, more than 35 bugs were closed on WebExtensions alone.

If you have authored an add-on in the past and are curious about how it’s affected by the upcoming changes, please use this lookup tool. There is also a wiki page and MDN articles filled with resources to support you through the changes.

APIs Implemented

The history API allows you to interact with the browser history. In Firefox 49 the APIs to add, query, and delete browser history have been merged. This is ideal for developers who want to build add-ons to manage user privacy.

In Firefox 48, Android support was merged, and in Firefox 49 support for some of the native elements has started to land. Firefox 49 on Android supports some of the pageAction APIs. This work lays the foundation for new APIs such as tabs, windows, browserAction in Android.

The WebNavigation API now supports the manual_subframe transitionType and keeps track of user interaction with the url bar appropriately. The downloads API now lets you download a blob created in a background script.

For a full list of bugs, please check out Bugzilla.

In progress

Things are a little bit quieter recently because there are things in progress that have absorbed a lot of developer time. They won’t land in the tree for Firefox 49, but we’ll keep you updated on their progress in later releases.

storage.sync

This API allows you to store some data for an add-on in Firefox and have it synced to another Firefox browser. It is most commonly used for storing add-on preferences, because it is not designed to be a robust data storage and syncing tool. For sync, we will use Firefox Accounts to authenticate users and enforce quota limits.

Whilst the API contains the word “sync” and it uses Firefox Accounts, it should be noted that it is different from Firefox Sync. In Firefox Sync there is an attempt to merge data and resolve conflicts. There is no similar logic in this API.

You can track the progress of storage.sync in Bugzilla.

runtime.connectNative

This API allows you to communicate with other processes on the host’s operating system. It’s a commonly used API for password managers and security software which needs to communicate with external processes.

To communicate with a native process, there’s a two-step process. First, your installer needs to install a JSON manifest file at an appropriate file location on the target computer. That JSON manifest provides the link between Firefox and the process. Secondly, the user installs the add-on. Then the add-on can call the connectNative, sendNativeMessage and other APIs:

chrome.runtime.sendNativeMessage('your-application',
  { text: "Hello" },
  function(response) {
    console.log("Received " + response);
});

Firefox will start the process if it hasn’t started already, and pipe commands through to the process. Follow along with the progress of runtime.connectNative on Bugzilla.

WebExtensions transition

With these ongoing improvements, we realise there are lots of add-ons that might want to start moving towards WebExtensions and utilise the new APIs.

To allow this, you will soon be able to embed a WebExtension inside an add-on. This allows you to message the WebExtension add-on.

The following example works with SDK add-ons, but this should work with any bootstrapped add-on. Inside your SDK add-on you’d have a directory called webextensions containing a full-fledged WebExtension. In the background page of that WebExtension will be the following:

chrome.runtime.sendMessage("test message", (reply) => {
  console.log("embedded webext got a reply", reply);
});

Then you’d be able to reply in the SDK add-on:

var { api } = require('sdk/webextension');
api.onMessage.addListener((msg, sender, sendReply) =>
  console.log("SDK add-on got a message", {msg,sender}); 
  sendReply("reply");
});

This demonstrates sending a message from the WebExtension to the SDK add-on.Persistent bi-directional ports will also be available.

Using this technique, we hope add-on developers can leverage WebExtensions APIs as they start migrating their add-on over to WebExtensions. Follow along with the progress of communication on Bugzilla.

There are also lots of other ways to get involved with WebExtensions, so please check them out!