A custom userChrome.css and userContent.css that rounds corners, and enables users to add a background to the default Firefox newtab page. This image is defined as image.png in the /image directory. I also enable use of a custom font in the Firefox UI. I use Poppins, which I will not distribute in this repository in respect to its creator, Indian Type Foundry. You may install any font you like within the /fonts directory, and you will need to edit line 4 in userChrome.css and line 6 in userContent.css accordingly.
NOTE: This userchrome.css is currently (partially) incompatible with the new sidebar tabs on Firefox, as the CSS selectors for both are the same.