penders - 9:08 pm on Jul 27, 2011 (gmt 0)
I still think the route cause is that empty clearing DIV. By giving it content, or if you clear the float by setting overflow:hidden on the parent container instead then you don't get this problem.
From a (rather old, and possibly out of date) article on PIE, "How To Clear Floats Without Structural Markup [positioniseverything.net]",....
...some browsers can have trouble with certain kinds of clearing elements in some situations. Mozilla is particularly sensitive to clearing problems.
...may be some things don't change?
What version of FF are people using? I'm actually running FF 3.6 at the moment.