Freiburg will face a slightly tougher opponent than Dortmund so the chances of Freiburg winning are not certain because Frankfurt are also trying to maintain their position in the Champions League places. And if one of them loses this weekend it will certainly give Dortmund a big advantage if Dortmund can continue their winning run at home to Holstein Kiel which is a weak team that Dortmund can easily beat. I hope Dortmund can return to the UCL next season with the current coach so Dortmund must try to win one of the UCL places this season.
You're right, I didn't even realise it earlier, Frankfurt too is fighting for themselves and as such they mustn't lose to Frieburg by all means, at least a draw will be very much ok for them. The point difference between them and Dortmund is 3 points and if eventually Frankfurt loses to Frieburg then they will be tied on points with Dortmund if Dortmund beats Holstein Kiel which is certain from all indications. So either was Dortmund will qualify if they can beat Holstein Kiel with at least 2 goals and above.