I noticed the differences font format between PC and Mac web browsers while I inputted my "Happy's <3 Day" in my Twitter to post the status in Facebook. The <3 change into a heart icon in Facebook:
Windows XP; Firefox 2.0 and IE6 browser
Windows Vista; Firefox 2.0 and IE7 browser.
Mac OS X; Safari 3.0 browser
Mac OS X; Firefox 2.0 browser
I figured out - Mac OS X Firefox 2 might have glitch or does not support font format. Hmm, take a note to Mozilla!