preferences/service

Access the Preferences system in Firefox. This enables add-ons to get and set system-wide settings. These are the same preferences that are exposed to users in the about:config page.
 
preferences/service gives you full access to the preferences system. You can also use the simple-prefs module to access just the preferences for your own add-on and expose them to the user in the Add-on Manager.

Globals

Functions

set(name, value)

Sets the application preference name to value.

Parameters

name : string
Preference name.

value : string,number,boolean
Preference value.

Example:

var name = "extensions.checkCompatibility.nightly";
require("sdk/preferences/service").set(name, false);

get(name, defaultValue)

Gets the application preference name.

Parameters

name : string

defaultValue : string,number,boolean
Preference value.

Returns

string,number,boolean : Preference value, returns defaultValue if no preference is set, returns undefined if defaultValue is not provided.

Example:

var name = "extensions.checkCompatibility.nightly";
var nightlyCompatChk = require("sdk/preferences/service").get(name);

has(name)

Parameters

name : string
Preference name.

Returns

boolean : Returns whether or not the application preference name exists.

defaultValue

Example:

var name = "extensions.checkCompatibility.nightly";
if (require("sdk/preferences/service").has(name)) {
  // ...
}

keys(root)

Parameters

root : string
Preference root name.

Returns

array : Returns an array of strings representing the child preferences of the root of this branch.

isSet(name)

Parameters

name : string
Preference name.

Returns

boolean : Returns whether or not the application preference name both exists and has been set to a non-default value by the user (or a program acting on the user's behalf).

Example:

var name = "extensions.checkCompatibility.nightly";
if (require("sdk/preferences/service").isSet(name)) {
  // ...
}

reset(name)

Clears a non-default, user-set value from the application preference name. If no user-set value is defined on name, the function does nothing. If no default value exists the preference will cease to exist.

Parameters

name : string
Preference name.

Example:

var name = "extensions.checkCompatibility.nightly";
require("sdk/preferences/service").reset(name);

getLocalized(name, defaultValue)

Gets the localized value for an application preference name.

Parameters

name : string

defaultValue : string
Preference value.

Returns

string : Localized preference value, returns a default value if no preference is set. Some preferences refer to a properties file. So that prefs.get returns the properties file URL whereas prefs.getLocalized returns the value defined in the properties file.

Example:

var prefs = require("sdk/preferences/service");
var name = "general.useragent.locale";
prefs.get(name); // is equal to "chrome://global/locale/intl.properties"
prefs.getLocalized(name) // is equal to "en-US"

setLocalized(name, value)

Sets the localized application preference name to value.

Parameters

name : string
Preference name.

value : string
Preference value, a URL to a properties file

Example:

require("sdk/preferences/service").set("general.useragent.locale",
                                   "chrome://global/locale/intl.properties");

Example: Setting Global Preferences

var { get, set } = require("sdk/preferences/service");
var { when: unload } = require("sdk/system/unload");

var oldValue = get("browser.urlbar.autoFill");
set("browser.urlbar.autoFill", true);

// By AMO policy global preferences must be changed back to their original value
unload(function() {
  set("browser.urlbar.autoFill", oldValue);
});