Thanks Timo for your answer :)
Yes the full path to the swf was there, so that wasn't the problem.
Anyway, I finally made swfAddress work in Firefox (hrm, not in iExplorer..). But after some experimenting with it I realised that its get-functions never returns the full URL (correct me if I'm wrong here).So, I think I skip the swfAddress-idea..
I guess passing the current page Href to the swf from the skin, as you said, is what I have to do. The big problem is that almost nothing like that will work in iExplorer for me.. query strings and flash vars sent directly to the swf will just work once at the moment. Any experiences with this? Maybe I should start a new thread about it.