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.
Experimental
Information about the application on which your add-on is running.
With the exception of ids, each of these properties exposes the attribute of the same name on the nsIXULAppInfo interface. For more information, see the MDN documentation.
Globals
Functions
is(name)
Checks whether the host application is the given application.
Parameters
name : string
A host application name.
Returns
boolean : True if the host application is name and false otherwise.
isOneOf(names)
Checks whether the host application is one of the given applications.
Parameters
names : array
An array of host application names.
Returns
boolean : True if the host application is one of the names and false otherwise.
versionInRange(version, lowInclusive, highExclusive)
Compares a given version to a version range. See the MDN documentation for details on version comparisons.
Parameters
version : string
The version to compare.
lowInclusive : string
The lower bound of the version range to compare. The range includes this bound.
highExclusive : string
The upper bound of the version range to compare. The range does not include this bound.
Returns
boolean : True if version falls in the given range and false otherwise.
Properties
ID
The GUID of the host application. For example, for Firefox this value is "{ec8030f7-c20a-464f-9b0e-13a3a9e97384}".
name
The host application name. The possible values here are:
"Firefox""Fennec""Mozilla""SeaMonkey""Sunbird""Thunderbird"
"Firefox"and"Fennec"` are the most commonly used values.
version
The host application version.
platformVersion
The Gecko/XULRunner platform version.
ids
A mapping of application names to their IDs. For example, ids["Firefox"] == "{ec8030f7-c20a-464f-9b0e-13a3a9e97384}".