This changes everything on that scripting.com page to Comic Sans for me:
* { font-family: "Comic Sans MS" !important; }
I'm using Stylish 1.0 on Chrome 23.0.blahblah and 1.3.something in Firefox 18. (Amusingly, that line causes the MENUS in Firefox to be rendered in Comic Sans!)
Are you sure that your CSS override is correctly worded? Are you using a different version of Stylish?
Okay... You're overriding font-family, not font-size or any other parameters. This means that you'll override the font shape, and no other parameters. If you really need to have a particular font to help you function despite your condition, then you really gotta ensure that you have it.
What limited knowledge I have of CSS selector precedence tells me that a top-level override is the only way to ensure that the fonts that you require to be able to read the internet without raging are applied.
Are you sure that your CSS override is correctly worded? Are you using a different version of Stylish?