webdriverio tests are basically automation tests similar to selenium tests. Looking at FIREFOX PROFILE SERVICE(http://webdriver.io/guide/services/firefox-profile.html), it looks like you can only fire up the extensions, but not define actions like click or type. If that would have been the case, One could have intercepted the requests, defined their own response and have automated tests defined for an app/website. Have a look at the blog post to understand the proper use case.