You are right, it has something to do with the Helvetica Neue (which I have installed, Mac TrueType I think).
Chrome behaves well when I deselect the font-family preference in the HTML inspector window (shown below) and also when I just delete 'Helvetica Neue',
in the css.
My Firefox definitely shows the inputfields in Neue Helvetica (doublechecked in Firebug).
Backend goes alright in Safari, but in Safari text looks like a (plain) Helvetica or Arial to me. (no 'Safari-Firebug-installed', so cannot check)
So maybe a -webkit-font-family without Helvetica Neue as last resort? Strange, though...