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Preferences in Activity Stream

Preference branch

The preference branch for activity stream is browser.newtabpage.activity-stream.. Any preferences defined in the preference configuration will be relative to that branch. For example, if a preference is defined with the name foo, the full preference as it is displayed in about:config will be browser.newtabpage.activity-stream.foo.

Defining new preferences

All preferences for Activity Stream should be defined in the PREFS_CONFIG Array found in lib/ActivityStream.jsm. The configuration object should have a name (the name of the pref), a title that describes the functionality of the pref, and a value, the default value of the pref. Optionally a getValue function can be provided to dynamically generate a default pref value based on args, e.g., geo and locale. For developers-specific defaults, an optional value_local_dev will be used instead of value. For example:

{
  name: "telemetry.log",
  title: "Log telemetry events in the console",
  value: false,
  value_local_dev: true,
  getValue: ({geo}) => geo === "CA"
}

IMPORTANT: Setting test-specific values for Mozilla Central

If a feed or feature behind a pref makes any network calls or would other be disruptive for automated tests and that pref is on by default, make sure you disable it for tests in Mozilla Central.

You should create a bug in Bugzilla and a patch that adds lines to turn off your pref in the following files:

  • layout/tools/reftest/reftest-preferences.js
  • testing/profiles/prefs_general.js
  • testing/talos/talos/config.py

You can see an example in this patch.

Reading, setting, and observing preferences from .jsms

To read/set/observe Activity Stream preferences, construct a Prefs instance found in lib/ActivityStreamPrefs.jsm.

// Import Prefs
XPCOMUtils.defineLazyModuleGetter(this, "Prefs",
  "resource://activity-stream/lib/ActivityStreamPrefs.jsm");

// Create an instance
const prefs = new Prefs();

The Prefs utility will set the Activity Stream branch for you by default, so you don't need to worry about prefixing every pref with browser.newtabpage.activity-stream.:

const prefs = new Prefs();

// This will return the value of browser.newtabpage.activity-stream.foo
prefs.get("foo");

// This will set the value of browser.newtabpage.activity-stream.foo to true
prefs.set("foo", true)

// This will call aCallback when browser.newtabpage.activity-stream.foo is changed
prefs.observe("foo", aCallback);

// This will stop listening to browser.newtabpage.activity-stream.foo
prefs.ignore("foo", aCallback);

See toolkit/modules/Preferences.jsm for more information about what methods are available.