This thread's gone all over the place...
Op, why do you have to deal with the teen? Your husband has done the wrong thing, why is he not dealing with his son's reaction?
Also, it sounds as if you need to work out what your own view is of porn - the litmus test is: if you think it's a healthy thing, you would suggest to your children it's a great career for them. If your reaction is no way, I'd want something better for them, then please don't present it as a good/healthy/normal thing to an impressionable teen. Once you know what you think about it, you'll be in a better position to discuss with your son.
'Enraged' sounds like your son was revolted by whatever your husband was looking at - do you know what the film was of, has your son told you or have you watched it? If not, what if it was teen boys your husband was looking at? Or schoolgirls and old men? Consider whether you'd still be keen to present porn as a healthy normal activity to your son.
Finally, please don't link masturbation and porn, as if they always go together. Masturbation doesn't require porn as most individuals have some imagination.
Seconding the pp who suggests the husband leaving this on the family computer needs more investigation.