The “of” biz caught me years ago when I was first given this test. These days, I remember the trick, and so look out for those pesky disguised effs.
Nice to be a genius for a couple of seconds, tho’. 
I got forty-three. I’m a sooper genius.
FFFFFFFFF
FFF
FFF
FFFFFFFFF
FFF
FFF
FFF
FFF
FFF
Now, riddle me this ‘sooper genius.’ How many F is that?! Bwahahahahaha…
My band teacher presented this to us in seventh grade as an exercise to demonstrate the importance of reading music carefully and not to overlook such little details. Most of the class (including myself) only counted three F’s.
Thank you, I believe I missed one of those. That’ll teach me to read with only one contact lens in. So I’m not stupid, just half-blind.
I got four the first time through because I missed the middle two 'of’s. If this were the Cracker Barrel peg puzzle, I believe that would make me Just Plain Dum.
Wow, I got three, and I swear to God I went through that letter by letter TWICE.
I’m impressed.
I’m pretty sure though that most all of the people who got 6 (me included woohoo!) would not count 6 if we weren’t challenged from the beginning to not fall into a trap.We’re tipped off to be especially careful not to miss anything tricky. I tried it later, going faster and not “zoning”, and I missed a couple, a few times in a row even