Thank you for your reasonable replies, all of which touched on things she and I have discussed. Yes, she accepts a general, background level of 'visual erotica' as standard fare for males even in the most satisfying, healthy relationships, but her concern was that he was ogling while home alone with the girls.
She and BF had a frank discussion, and, while he was affronted that she would even have an inking of a concern, she calmly pointed out that, when it comes to one's children, one is ALWAYS going to be on the alert for any potential dangers. Turns out that she was wrong about
when he was looking at
what, and he assured her he would not be surfing when the girls were at home.
On the other hand, he's now irritated that she snooped through his browsing habits, and there's still that 'gut' feeling of wariness. They ended up having a good discussion about the basic level of trust/distrust in their relationship (based upon some earlier stuff for both of them -- completely unrelated to any of this), and seem to be heading in the right direction.
Thanks again, Cellarites, for your thoughts, and for not jumping all over my friend for any perceived inadequacies on her part.