[horde] Firefox fails on login via horde 3.2.1

[Ralf Hornik Mailings]

Hi list,

after upgrading to horde 3.2.1 and the other applications (that solved 
my csv import issue in turba) I noticed, tha I cannot login to imp (4.2) 
using mozilla.
Authentication is successfull (auth.log), but the login prompt returns.

However there is nothing documented about issues with mozilla. Can 
somebody reproduce that and give any hints?
Thanks and best regards

Ralf