I have changed the font on my OS/2 firefox (no problems). Otherwise, testing from the Windows XP machine Firefox, Internet Explorer, Chrome and Safari all are using whatever font they shipped with.

Incidentally, the rendering engine is at least part of the problem. While Chrome has been error free when the page is loaded in a window, I reloaded in full screen mode and Silver Pomfret was out of place, otherwise all correct, so margins matter there too, just not so much.