where is the firewall on a 2012 jeep liberty jet

The firewall is the sheet metal between the engine and the passenger compartment. The sun visors are not in the firewall.

RIght, if you have a sunroof, you want to look for the sunroof drains that are located inside the sunroof frame. They get blocked with dirt over time. You will need to clear them. If you don't have a sunroof, then I would suspect the windshield seal is compromised.