As it is explained in bug 85994 comment 14 , when seeking on a media from a server not supporting "Range" requests, our "webkitwebsrc" is not able to deal with a "200" response when it is expecting a "206".
Actually, doing some bureaucracy and changing the chain of dependencies ...
As the title says, it is not possible to play the sound in http://www.playmapscube.com
This is working fine here in MiniBrowser. Please reopen if needed.