After creating a new Theme for http://www.tegeljudo.de I found the problem, that slideshows are not shown when using FireFox 11/12 with Windows.
No problems to be seen with Internet Explorer 9, Safari and Firefox for OSX (and - very interesting - Firefox running on XP-VM with OSX).
The space for the slideshow is emptied, no hint for the need of downloading flashplayer, no error.
If the option "use flash on all mobile devices" is disabled, also FireFox is showing the slideshows.
As the flash slideshow has more options, I would like to continue using it.
Does anyone has similar effects or - what would be better - a hint on a solution?
Thanks in advance!