It does funny things with a DIV with nothing but an empty P tag pair in it.
I know empty P constructs are discouraged, but it is the only trick I've been able to find that allows me to terminate a set of left floated DIVs on Netscape 4.x without having it mangle the page completely.
Previous versions of Mozilla (and any other browser I've been able to throw at this) ignored the construct as they should and put the next DIV at the left margin, below the floaters.
Mozilla 1.3 sticks the DIV following the empty construct to the right of the floating DIVs instead of going below them...