According to NameNerds.com (which is not entirely reliable, mind), it's pr. FWAY-lawn. Also, a comment on Faolán's entry says it's FEH-lahn, but the comments section attracts a lot of... inaccuracies, shall we say.
At any rate, the O is definitely not pronounced.
Proud adopter of 15 punctuation marks; see my profile for their names.