When visitors come to St. Agnes Church they often comment on the fact that the clergy wear birettas. The biretta used to be obligatory on the part of the priest celebrant and deacon and subdeacon. Now it is an option, and a good one. Of course it is necessary to use the biretta properly. This is what I call "birettiquette".
Here is an example of proper use of the biretta during Mass. When the Holy Name of Jesus is sung or spoken the clergy uncover, usually lowering their biretta to their right knee, and then cover again. Here are a couple shots.
The celebrant in the photo is the relatively well-known and controversial Fr. Robert Altier, assistant at St. Agnes Church. Father was very much in the news a few weeks ago.