How do I set the .PDF viewer in Safari?

I have Safari set up to open .pdf documents in a browser tab. Currently it uses Adobe reader to do this. I'd like to change it so that Skim is used to view .pdf files in a tab instead. Skim is already my default .pdf viewer in Finder.

Is there a way to specify which .pdf app to use in Safari? I poked around the Preferences, but I couldn't find anything.