Changing icons in the "favourites" box

["W. Martin Borgert" <debacle debian org>]

Hi,

in general I don't care about icons, but sometimes, I'm not
happy with the default ones: My favourite mail client is named
after a dog, so the icon displays a dog. However, this joke
works only in English, most other users can't understand it. And
I really don't want a dog on my desktop :~)

How can I change application icons in GNOME3?

TIA!