How to Read User Agent in AddOn Script?

Add-ons Development
1

I was wondering if anyone knew how to read the browser user agent from the AddOn script (not content script). I tried reading it using the preferences/service object:

var prefs = require("sdk/preferences/service");
var userAgent = prefs.get("general.useragent");
//userAgent is undefined

but I can’t seem to find a preference value that will serve up that information.

2

window.navigator.userAgent is the user agent, with caveats.

  1. It is considered non-standard and the recommendation is not to use it. It is still supported by all the main browsers, but you may get deprecation warnings.

  2. It may not be the user agent sent in http headers. The preference general.useragent.override will be used in http headers, but not in window.navigator.userAgent.

nsIHttpProtocolHandler defines a userAgent getter which will give you the one that goes in the http header. Most of the time! The general.useragent.override preference takes precedence.

There is an interface nsISiteSpecificUserAgent which has a method GetUserAgentForURIAndWindow(). You might try calling this yourself, which is what the navigator.userAgent getter does if there is a specific window and URI. If there is no window or URI, or no site-specific override, then the protocol handler is used.

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