You can override the user agent in your moov_config.json file, by adding an entry similar to the following:
"user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_4) AppleWebKit/536.25 (KHTML, like Gecko) Version/6.0 Safari/536.25"
The user agent that gets sent from Moovweb to the upstream site will now be the one specified above. By default when this is not added, the user agent that gets passed along will come directly from the browser. This allows you to specify the override.