There are applications that work differently depending on the web browser and devices from which they are opened. It is not possible to have all browsers, versions, and devices to test them. But, all of them are identified by a parameter included in the HTTP request, named the user agent. This User Agent parameter can be switched directly in the HTTP request using an HTTP proxy, but to make our lives easier, it is possible to use User-Agent Switcher (https://addons.mozilla.org/es/firefox/addon/user-agent-switcher/), a Firefox add-on that has a lot of user agents to analyze different responses.