User-Agent Switch for Opera

First need to know what is user assign thing. UserAssign is your userassign based on what type of drive or operating system you are using. If you are a os user and on top of that you are using browser then os browser is your userassign.

A string that identifies the browser accessing a website is known as a useragent in JavaScript. The server uses this string, which is sent as part of the HTTP request, to decide which version of the website should be served to the user.