DNS Cache Problem

I'm having a problem accessing Facebook on my MBP. Every other site works, but if I try to go to Facebook.com, it just sits there as if it is loading. I've had this problem once before, and flushing the DNS cache ($dscacheutil -flushcache) fixed it. But this time, the problem is returning every few hours after I flush the DNS cache. Only Facebook is affected, no other sites. I cleared Firefox's cache, and that had no effect.

Is there something I can do to fix this?