Well, that didn'T work.
First error message now was "nicht wohlgeformt" (is in word by word translation in English "not well formed").
(A second error message of course followed then saying "MyThis.tempObj.links has no properties" )
Instead of text/xml i just tried text/html too, but that gave an exception with "NS_ERROR_NOT_IMPLEMENTED" at the parseFromString-function.
Could I use setMimeHeader? But I read that only working in IE. (I'm using Firefox.)
Thank you already for all your help!
Actually I started first by retrieving the links by regex-functions from the source of loaded iFrame, but everyone suggested to just use XMLHttpRequest instead. Really, Firefox doesn't seem to have a simple function to get the source of a loaded website/window/document/iFrame/Frame. So now I tried to use XMLHttpRequest and the links-property and it doesn't work again.