Marco posted about some of the quirkier unicode glyphs, and notes:

The characters differ from browser to browser in terms of appearance. I have no idea why this is. Fascinating!

The characters vary because Firefox and Safari use different font rendering engines — Firefox of course being non-native to Mac OSX.

Most unicode glyphs don’t exist in every font, so an intelligent text rendering system, such as that in OSX, will swap a missing glyph with one from another font, rather than displaying mojibake.

Because Firefox and Safari have different text layers, they pick different typefaces.