Tutorial on installing Git css for Firefox

I’m not familiar with doing manual installs to a browsers profiles folder to alter the browser cosmetics. I am trying to follow Aris-t2’s instructions to install into Firefox 57 (and later) the .css codes to bring back the (Noia) theme I used to use for the browser before it went thru a change in code. I’m missing something in the procedure that I am following to get the browsers profile to recognize what I have entered to change the profile to what I am looking for. I have created the *chrome* folder as instructed as there is not a chrome folder there, I have copied the CSSforFX files to that folder but something must be missing as the browser is not recognizing the input? Can anyone assist me? https://github.com/Aris-t2/CustomCSSforFx