No about::config on gecko browsers?

I dont quite understand what is causing this but on arch i installed some random css thing or whatever but i literally cant get to it. Which was beyond bizarre so i went for FF to check and still i get the same result. Im unsure if this is a linux package problem or some new firefox policy but i cannot, for the life of me, find anything even related to this on google and ai essentially keeps telling me to just type about::config and just kinda pray it would work. Below is an example of what i mean happens when inputting it!

https://preview.redd.it/l3n8mq52yime1.png?width=886&format=png&auto=webp&s=f1df62b4e1f0cf8de7778ef4229d54e5b4504662