Definition of CSS clause ".codebox code" appears to be faulty. This is typically in styles/prosilver/theme/content.css, and contains the line:

font: 0.9em Monaco, "Andale Mono","Courier New", Courier, mono;

Shouldn't this be:

font-family: 0.9em Monaco, "Andale Mono","Courier New", Courier, monospace;
?

This was reported by a user of the Raspberry Pi forums who uses a legacy browser (NetSurf) on even older systems.