theme looks different in different browsers

hey, my blog is at, http://eckline.com

In fire fox my theme looks the way i want it to, but the drop down menu does not work.

In internet explorer the content section width is different and pushed more to the right. and the drop down menu is more messed up.

In google chrome, it looks perfect. everything works fine.

so my question is, how do i make everything work like it does in google chrome.