Returns list of available browsers & OS.

def browsers(self, browser=None, browser_version=None, device=None, os=None, os_version=None):
        """
        Returns list of available browsers & OS.
        """
        response = self.execute('GET', '/screenshots/browsers.json')
        for key, value in list(locals().items()):
            if key in ('self', 'response') or not value:
                continue
            response = [item for item in response if match_item(key, value, item)]
        return response