How to set a custom user agent using selenium web driver (Sauce Labs)?

I'm running my selenium tests through Sausage (which basically extends the phpunit selenium test case to include additional functionality for Sauce Labs). My issue is I need to run a specific user agent on Firefox.

Here's my firefox browser array:

        array(
            'browserName' => 'firefox',
            'host'        => 'localhost',
            'port'        => 4444,
            'local'       => true,
            'sessionStrategy' => 'isolated'
            )

Solution

The trick to getting this is creating a firefox profile which contains the user agent. Then we pass the profile to the web driver as a desired capability.

The following commands create a firefox profile and base64 encodes it so we can pass it to the web driver.

mkdir firefox-profile
cd firefox-profile/
echo 'user_pref("general.useragent.override", "Mozilla/5.0 (iPhone; CPU iPhone OS 6_1_4 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/6.0 Mobile/10B350 Safari/8536.25");' >> prefs.js
zip -r ../firefox-profile.zip *
base64 < ../firefox-profile.zip

The simplified code with the base64 encoded firefox profile is below:

      array(
            'browserName' => 'firefox',
            'host'        => 'localhost',
            'port'        => 4444,
            'local'       => true,
            'sessionStrategy' => 'isolated'
            'desiredCapabilities' => array(
                'firefox_profile' => 'UEsDBBQAAAAIAOKTikaRRkklnQAAALQAAAAIABUAcHJlZnMuanNVVAkAAyhPKFUoTyhVVXgEADIE
MwQljMsOgjAURPd+xU1XkJAWxDYmrNSFJthIgq8dKXjRhoaSAi78elF2MydnZuzRFZ3D2iNPbNEp
Q8cJqakM1L7ROf1AEgCR9qONUYzTEDydvWyLCeyyC8wZTjmIIipWYHSDIFX1I3cfNl1n8IZlqgfG
Y0GXArz0cJbHYDb3WDXWhyu6XtuWiele2lIbZFG4jXkIuaqV02z9H3PiJ4svUEsBAhcDFAAAAAgA
4pOKRpFGSSWdAAAAtAAAAAgADQAAAAAAAQAAALSBAAAAAHByZWZzLmpzVVQFAAMoTyhVVXgAAFBL
BQYAAAAAAQABAEMAAADYAAAAAAA='
                )
            )

Thanks to Malvineous from a related thread for the idea: PHPUnit + Selenium: How to set Firefox about:config options?

For reference, this is the list of allowed desired capabilities: https://code.google.com/p/selenium/wiki/DesiredCapabilities