If you have a look here -> http://www.idmk.nl/kaal.html, and click on one of the links on the left side, you will see the problem in FF.
The pop-up slides underneath the box. Removing the overflow:auto on the .cursuskalender fixes the issue, but I do need the overflow:auto on that div. So removing it isn't an option, but how else to fix it? I try'd giving to pop-up box a z-index of 9999, but that didn't fix the issue either.
This way its coded wasn't my idea, but I do have to fix it now...
Any idea how to get this to work properly in Firefox?