IDP3.2.1 Unable to decode incoming request

[Peter Schober]

* Käfer Thomas <thomas.kaefer at fh-campuswien.ac.at> [2016-07-12 13:33]:
> 2016-07-12 12:14:20,908 - ERROR
> [org.opensaml.profile.action.impl.DecodeMessage:73] - Profile Action
> DecodeMessage: Unable to decode incoming request
> org.opensaml.messaging.decoder.MessageDecodingException: This
> message decoder only supports the HTTP POST method

You're sure the SP causes your browser to sent an HTTP POST request
there, not HTTP GET? Is that a public SP I can test myself?
(Of course that doesn't explain other browsers working, just something
to get out of the way.)
-peter