All the links at the top of the page (ie, link to blog, contact, review, classes) and the text below "for a beautiful web" show up as boxes with numbers in them

All the links at the top of the page (ie, link to blog, contact, review, classes) and the text below "for a beautiful web" show up as boxes with numbers in them. Is this some font or other problem on my system (Ubuntu 9.04 + Firefox 3.5 beta 4) or are other people getting it as well? I see them once in a while on other sites, and it's pretty annoying.