userChrome.css tutorial

<h2>How to install userstyles in FX 57+?</h2>
<ol><li>Go to <b>about:support</b>, click the button <b>Open folder</b></li>
<li>Create a folder called <b>chrome</b>, inside that make an empty text file called <b>userChrome.css</b> (make sure it doesn't end with .txt!)</li>
<li>Select the style options you want, then click <b>Show CSS code</b>, copy the field contents</li>
<li>Paste the contents to the userChrome.css file and save it. Make sure the <i>@namespace</i> row appears only once, at the beginning!</li>
<li>Restart Firefox to see the changes.</li></ol>
If you already have the file, simply open it and add new code to the end (tutorial steps 3-5).