So it's not possible from a fork, if you've only added the original repo as your single remote?

Currently I add the random person's fork as a remote to inspect/modify their PR branch. Was hoping for some GitHub magic to eliminate this step.

It is possible. You can specify a URL instead of a remote name for `git fetch`.

I thought it was in the PR destination repository (since they are under that repository's /pull namespace). You'd need to add the alternate remote if it's a PR into a fork (as opposed to from it), no?

You are absolutely correct. My apologies, as I understood the problem as "I have a fork and want to receive pull requests".

This can be a pretty common setup for some git workflows. Everybody makes a fork and takes / pushes pull requests or branches from their fork to others. The main advantage would be that if you have a lot of branches they don't all have to be on upstream and you don't need to have upstream permissions for everyone to push branches or changes to.

Nonetheless, I can see why my comment raised some confusion.