Success! - kind of.
I re-downloaded the steam app and copied it into my applications folder (replacing the old one in the process). When I launched steam it downloaded an update. FM then started no problems! I quit to make sure it wasn't a one-off (as I'd read elsewhere).
Steam then asked me...
I'm having the exact same problem right now (am in Aust.). Am trying to re-install at the moment. Tried re-verifying cache/killing steam through activity monitor etc. as suggested in other threads but no luck.
It was very late and I was quite bleary eyed when I quit the game last night but I...