Why use .js extension if it does not even support what Javascript is supposed to support. Here is my user.js file that does not work in Firefox: https://pastebin.com/QZXL0YJp
However the following works: https://pastebin.com/xEjh7g9U
I wonder why not implement a full Javascript engine to read in those configuration files, it kind of sucks to keep on typing user_pref( in every line when one could put all the configs in a list and loop over it and use user_pref() to apply them.
https://stackoverflow.com/questions/10602504/how-does-user-js-work-in-firefox-in-detail:
It just looks like a JavaScript file. Once upon a time in Netscape 3 and maybe 4 it actually was, but now it’s just a file with a .js extension and a very restricted syntax that’s parsed by a separate (non-JS) parser and not executed in any way.