Your heater core sprung a leak. Not sure how to replace it (never had the opportunity on the Beast)
Also please post in 1 section
Yeah, I'm sure Shadow D is right.
You'll have to drain the antifreeze and properly dispose of it, or you could reuse it if it is relatively new.
You'll need to disconnect the heater core hoses, and work from both inside the engine compartment, and inside the cab to get all the screws off that need to come off. IF as you are doing the job, you find that the screws are different lengths, you may want to draw a picture and label which screws go where.
you may also want to label your heater hoses so that they go back properly, and or take pictures.
I have only done a few of them, and none on a bronco, but I recall once that it was a particular b*tch of a job, and one of the screws, just wouldn't come out, or I couldn't get to it, to get it out, nonetheless, I ended up breaking the houseing, and resealing it with caulking compound, or epoxy glue.
Have fun.
It's a bit of a pain of a job, but you'll have a feeling of accomplishment when you complete it.
joe