2003 Dodge Dakota condensation leak

When using a/c, condensation leaks onto passenger
floorboard, soaking carpeting. When I pulled up
carpet to find leak there was a quarter inch puddle
that seemed to come from behind rubber covering
over interior firewall. I'm not sure how long this
leak accumulated before I noticed it, as I commute
90 miles per day for work and use a/c daily as its
been over 90 degrees and humid for about 2 weeks.
What is the most likely source of this proble?