How Can I Distinguish Read and Unread Messages, When Both are Bold?

I'm trying to get Thunderbird working on Windows. I can't read thin faint Windows-style font rendering. I can set * {font-weight: bolder !important;} in userChrome.css, but since Thunderbird relies on boldness to distinguish unread and read messages, I'd need to find another way to distinguish these. I also use MacType, but it doesn't seem to affect Thunderbird or Firefox. As far as I can see, either 1. if the css can distinguish unread and read messages, maybe I could set extrabold and semibold, or I could set different colors. Or 2. I could set a bolder font with good-enough script support.