Works in Safari, not in Firefox, possibly jetpack

Hey, here’s a fun one:
I have a WP site that runs as smooth as ever in Safari, and returns a 500 in Firefox. The last major thing I did before this started was updating jetpack. Pinging the site works just fine.

Anyone who, unlike me, has anything to constructive to say about something like this? I’ll be glad to supply more info, I’m just not sure what exactly would actually be useful.