Yep I’m hosting the fonts myself.
Sorry to say I cant remember the link I followed on google but basically someone had a similiar problem with fonts on fonts.com. The support asked if a plugin is installed which let them change the UA String… That was the reason for him. So he completly uninstalled the ua changer (or whatever it was called) and hacked the firefox config setting the ua stuff back.
For me its still not working something must be wrong with my local installed firefox (config or whatever). I was setting up a VM and tested it from there everything is alright.