Hi Justin, (sorry for my English)
thank you for helpfull hints. I did a lot of investigation in a VM with a fresh Windows 7 and Firefox installation. The result was the same and the error was still there, but no errors were reported in the developer concole. In the "Network" output I saw, that the processing stopped after the first "Post XHR":
POST XHR https://www.mydomain.de/webtop/facade/ftajax.cfm?/ajaxmode/1/formtool/Image/typename/dmImage/fieldname/fc1E9D1B607B3311E69328000C2995D0A8SourceImage/property/SourceImage/objectid/1E9D1B60-7B33-11E6-9328000C2995D0A8/check/1 [HTTP/1.1 200 OK 143ms]
At least I've tested without using the SSL connection and everything worked fine !
Because the customer has no SSL cert for his website (not needed), I use a self-signed cert, for a SSL secured webtop login. In Firefox I've added this self-signed cert as an permanent exception. Normally this should work in Firefox, but in the case of image uploads in FarCry it does not work.
At the moment I have no idea how to solve this problem.