I'm hoping there's a preference toggle that I accidentally changed.
Did you check you have the quality of previews set to always HQ (little checker icons top right Bridge windows)
It's definitely a puzzle. (Version: Bridge CS6 5.0.1.21)
It seems a puzzle, but my version of Bridge CS6 is 5.0.2.4 so check for updates first.
The manual replacement of ACR was for MacOs Mavericks and Bridge CC
What computer specs do you have (RAM, VRAM, free disk space etc) and what OSX are you running?
Can you provide a screenshot of your Bridge window?