Enable Loading of userChrome.css and userContent.css in Firefox

How to Enable Loading of userChrome.css and userContent.css in Firefox

Starting in Firefox 69, the browser does not load userChrome.css or userContent.css by default. Users who use these files to tweak and customize their Firefox may want to re-enable them. Thankfully, it is easily can be done. There is a special option you need to turn on the about:config page.