If you are a Linux user. Really. It makes a big difference.
apt-get install msttcorefonts
msttcorefonts suggests you install the ttf-liberation package which contains "free variants", but in my experience, they do not work.
After installing msttcorefonts, with a website specifying the defaults:
/* http://www.sitepoint.com/article/anatomy-web-fonts */
font-family: verdana, "trebuchet MS", helvetica, sans-serif;
suddenly the displayed fonts look a lot better in both Firefox and Opera.