Comment 3 for bug 888814

A few notes on the new CSS:
WebCore/css/html.css (the "user agent stylesheet" in the inspector) has the following rules which serve as a pretty good guideline to which elements should be monospaced:

tt, code, kbd, samp {
    font-family: monospace
}

pre, xmp, plaintext, listing {
    display: block;
    font-family: monospace;
    white-space: pre;
    margin: 1__qem 0
}

So I'd suggest using those sets of elements for monospace, and using just "body" for proportional, as body * will only apply to subelements of the body, but not text in the body itself.