Useing with the Stylus add-on (addons.mozilla.org/en-US/firefox/addon/styl-us/)

Created a new style, added the code provided by the developer, set up a filter to work with URLs on domain x.com and Urdu text is now rendered in Awami Nastaliq.

All good.

I am pretty sure that this works but I am confused how to it up. I am a computer noob, so i don't know how to setup the user style you mentioned in description. Please help me.