Every comment block will have a monospace font toggle button added to the toolbar.
Clicking the toggle button will change the textarea font from the default font to a monospaced font.
When the monospace font toggle is active, the following css is applied:
font-family: Menlo, Inconsolata, "Droid Mono", monospace !important; font-size: 1em !important;
This code is integrated into the GitHub Dark Script; it is available here separately. There is no need to install both.