The user agent string is part of the header of any HTTP request and tells the webserver about the type of browser and about the operating system.
In Firefox it can be set by navigating to about:config
and adding the entry general.useragent.override
.
Here is an example user agent string for a Linux desktop system:
Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:15.0) Gecko/20100101 Firefox/15.0.1