Interesting css error with firefox

when make the body tag "float", everything mass up...... That's true
body cl*ss="interesting"

in css file:

interesting {
float: left;
}

guess what, the whole page's layout will be changed, especially padding and margin....
I have discussed this with Tim, but still don't know exactly the reason.

I guess this is a kind of bug in firefox when it tries to compile FLOAT tag