Some ideas:
- Do the bookmarks have any extra info? For example the links to the HULU pages. Do they contain parameters (such as ?campaign=fb) which could point to the origin of the bookmarks? - Try to reproduce. Remove/save some bookmarks, and visit the same pages you visited before (esp. FB) and see if the bookmarks reoccur. - Use little netstat to monitor connections. See if you spot something odd. But this is an time-intensive method.
It can be spooky when odd things like these happen on your pc. But many times it is just a confluence of circumstances. You could see this as an incident - when it reoccurs, then you have something to research. At that moment, put it on superuser or the likes. Probably you get better answers then here :)