Oh god, I have yet to figure out what it even wants. I assume it is asking me to close firefox to run an update, but I do and nothing is run. And apt upgrade doesn't somehow catch it?

It's amazing that they're managing to make it so confusing that someone who wrote .xsession files can no longer understand it without doing a bunch of research. This shouldn't be tricky... that message, in particular, is absurd. Why would you show that and then not have a button that says "update"?