Hi Nico,
What do you mean by "I can't click on any Tab"? - do you mean that when you click the tab it doesn't do anything? e.g. it does not navigate?
What operating system are you using? Is it Safari on Windows or Mac OS?
If I were you I would check the PAM: http://service.sap.com/pam if you look at the browser support Safari isn't supported on windows:
For IE9 have you tried running in Compatibility mode?
Hth,
Simon