Frizzle is incompletely dominant, not recessive. Incompletely dominant basically means that there is a dosing affect: one copy (F,f) displays less than two copies (F,F).
A bird with two copies is referred to as a curly, and the feathers tend to be very brittle and break. A bird without visible frizzling does not carry the gene.
That said, there is a recessive frizzle modifying gene, mf. If, and only if, a bird has two copies of this modifying gene, frizzling is reduced--sometimes to the point that a het frizzle (F,f) has little visible appearance of frizzling and a hom frizzle (aka a curley, (F,F)) has the appearance of an unmodified het frizzle.
