Contact form broken on Firefox

Hi,
I just found out that the German version of my contact page doesn't work on Firefox, but the English does. Weird. Any idea how to fix this?

Bests,
- Mathis

Sorry, forgot the link:
http://mathis-nitschke.com/wp/kontakt/

Hi,

It doesn't work on Chrome also, but the link is not correct I think;
When you are on this page: http://mathis-nitschke.com/wp/kontakt/ and click "English" the source URL is:
http://mathis-nitschke.com/wp

I guess you didn't really understand what I meant what didn't work. The page didn't load correctly. Just as I wanted to cerate a screenshot now I see that it works again. Very weird. Maybe it was a caching problem curated by plugin updates I did after posting here.

Thanks for checking in! And you're right, it would be nicer if the "English" button in the menu would direct to the current page in the other language. Currently it just directs you to the English homepage.

Bests and thanks!
- Mathis