FBTest for @-rules
http://code.google.com/p/fbug/issues/detail?id=5262
http://code.google.com/p/fbug/issues/detail?id=5289
http://code.google.com/p/fbug/issues/detail?id=5290
http://code.google.com/p/fbug/issues/detail?id=5429
http://code.google.com/p/fbug/issues/detail?id=5912