It means that the quality is excellent or "first class" (i.e. of the best quality or in the highest division of quality).

While I haven't found a source for "first quality", there is a defintion for "first quality workmanship" in [US Legal definitions](http://definitions.uslegal.com/f/first-quality-workmanship/):

> first quality workmanship means construction which is free from any defect materially affecting appearance or serviceability.