I think it's fair to say that many Falcons fans are not expecting a win in this one, given their recent struggles and the caliber of the opponent.
Atlanta is home, they're technically favored, and on paper the Vikings' offense is exactly the kind of offense the Falcons want to face in 2015, with a middling passing game and strong ground game that plays into Atlanta's defensive strengths. The Vikings are a tough team, though, and the Falcons have managed to keep games close but haven't shown any ability to win them over the last several weeks, so I can't blame anyone for feeling dubious about the outcome.