What should black do?

...against 3. Qf3 in the falkbeer countergambit?

Hmm, I don't know if I'd take a pawn as black.  f3 doesn't feel like a good square to use for the queen so I'd like her to stay there.  Also makes d4 feel weak.  I'm thinking Nc6... although I guess white plays Bb5 which helps him solve potentially annoying kinside development due to the queen on f3.

After 3...exf4 4.Qxf4 I wouldn't play 4...Qe7.  Again this just hinders kingside development.  4...dxe with Be7 and Nf6 and white is loosing a bit of time and his kingside is loose.  Plus with both center pawns gone black's development will be faster / easier in any case.  So actually taking the pawns seems to work out nicely for black.

f3 doesn't feel like a good square to use for the queen.

Which is one of the main purposes of this thread!!