Hi Collin:
I couldn't help jumping in here as hewing was my favorite sport for quite a number of years.
As Mark said keep your axe as sharp as possible at all times not just to hew fir, it will give you better control, with less effort and will be more efficient.
We hewed quite a number of large hemlocks for a 3 bay barn, these were freshly cut, and squared 12 by 12 timber at 36 feet without any wane.
They worked well but you followed the proper proceedure of hewing ie: working from the top to the bottom on each pass.
We never did as Mark suggests using the axe backwards, I have no idea what or how this could be done safely, especially with a broadaxe's cutting edge bevelled one way, and we never used a slick during the hewing process, or glue or finishing nails, maybe I have missed something over the years!
I did though hew 50-- 8 by 8 timbers out of cedar and it was the toughest hewing of my career, cedar is a terrible wood to work with. I do know that many barns and log houses were constructed using cedar timbers, especially barns, I guess the extra effort paid off because of the longjevity of the timer being able to last the test of time. I can honestly say that I never hewed fir, but I do suspect that if it was worked green and in the proper orientation to the grain that it would not be too bad.
Well good luck--
The Northern hewer