Thanks for your reply.
I dumped my firefox cache and there was a json-property called "drm" with the value "flash access" near the rtmpe-url. I bought the third season of Hart of Dixie.
Yes, amazon also sends via silverlight. I tried to download the stream with ismdownloader (avc1-version) but all I get is
Code:
ERROR: Audio format 'Vendor-extensible format' is not supported!
So I thought I give it a try with flash, because I can download at least something. And afaik there is no way to download encrypted silverlight-streams. But it's pretty indifferent for me HOW I gain a playable file.