Square Avatars and Size

I managed to make the avatars square in the bbpress forums. But unfortunately I don’t know how to customize them for Posts (Preview and Post itself) and for Comments below the Posts.

For all of them I need them to be square, and for the Preview and the Posts actually a little bit bigger (standard seems to be 60×60).

In comments I want them smaller and square.

80×80 square for all would be good.