It seems that my menu bar is displayed with a different font stretch in Firefox than it is in Chrome. See the following:
Here is the CSS applied to this element:
font-variant: small-caps; font-size:13px; letter-spacing: 0px; font-family: Arial; font-stretch: normal; text-decoration: none;
As far as I can tell everything regarding that font is exactly the same, yet they still display differently (see pic).