How do i set it up to be able to use firefox proxys if I am...?

I'm behind a router shared by 3 other people. Is there any way for me to set it up so i can use the proxy setting of firefox and adjust it to access the internet. At the moment whenever i try to change the proxy settings of firefox, it wont allow me to access the internet afterwards. How do i set it up to be able to use firefox proxys if I am...?You shouldn't need to mess with proxy settings to access the internet. That's not what a router is. If you need to use a proxy, well, it shouldn't have anything to do with your router settings.