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.

This does not work in latest firefox Ubuntu version. The Urdu text on Twitter remains as it is after installing the font

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.