I'm working on a project where I wanted to use a pure CSS menu and
overflow: auto float clearing. Due to a bug this can't be done in Firefox 1.0.x when the child
ul of the menu overlaps the
overflow: auto block. This bug is fixed in the nightly though, and I hope it will be fixed in 1.1 as well.
For my project I'm going to assume that the main content
div will always be longer than the floating sidebar so I don't need to clear it.
There is a backup plan.
Update 2005-07-12: found a workaround.