Arial -> Roboto

ArialRoboto.user.css

/* ==UserStyle==
@name        Arial font replacement
@namespace   vivelin.net
@version     1.0.4
@description Replace Arial, Helvetica and similar fonts with Roboto. Requires Roboto to be installed locally. Available from <https://github.com/google/roboto/releases>.
@author      Vivelin
@updateURL   https://gist.github.com/Vivelin/cd37bbcee8caa00bd8eb5383f07667d6/raw/ArialRoboto.user.css
@license     unlicense
==/UserStyle== */

@font-face { font-family: 'Arial'; src: local('Roboto'); }
@font-face { font-family: 'Helvetica'; src: local('Roboto'); }
@font-face { font-family: 'Helvetica Neue'; src: local('Roboto'); }