ok So when you set the padding for the menu items you used ie. So now you need to set them so they work perfectly in firefox. Then use
.menu_item { padding: 5px; *padding: 7px;}
IE is the only browser that will read the selector after the asterisk. This means you can change this padding until it fits for IE.
This is a kludge. You can't count on any undocumented "feature" like this (actually a violation of standards). Software changes in either IE or in some other browser will cause it to fail. It also should not validate.
Despite what Midimagic says, you won't be able to set that up with percentages.
Why not? I do it all the time. The only time it won't work is if you mix nonzero surrounding styles with width styles.
Note that the left padding of the ol and ul tags is NOT zero. So to properly set width of these tags, you must nest them inside div tags, and apply the width to the div.
Good luck!