Don't let perfect be the enemy of good. A video call is obviously better for conveying voice, demeanor, and body language, than is written text in a forum.

I absolutely loathe when companies do the "let's jump on a call" thing, but this does seem like a pretty exceptional case where a call would be indeed very helpful. This is also an opportunity for him to get directly in front of people at Mozilla to voice his concerns. There's a high probability of impact here, which to me seems very much worth the 15 or 30 minutes or however long it takes to jump on a call.