Header problem in Fire Fox

In Fire Fox I have problems with the slider in the header (on the homepage). The white figures of the slider lie over the section-text of the page instead of underneath. I gave this section-text a negative margin, so it has to overlap the header.
This problem does not occur in Chrome. How can I solve this?

• This topic was modified 4 years, 7 months ago by nicolepluim.

The page I need help with: [log in to see the link]