AI OnAI Off
This is a known bug also occuring in Chrome for CMS 6 R2. See http://world.episerver.com/Forum/Developer-forum/Problems-and-bugs/Thread-Container/2013/8/Personalize-Content---Visitor-Group-Lookup-not-working-in-Chrome/
Doesn't seem to be a bug report for it though. Contact EPiServer support to hear if they have a quickfix.
I contacted EPiServer support, which referenced the list over supported CMS6 R2 browsers for edit-mode:
Unfortunatly, my client will most likely be auto-updated to IE10/11 and newer Firefox versions.
I was experiencing this same problem and I have a "fix." It isn't the most elegant solution but it does work with IE 10, Firefox 25, and Chrome.
I noticed that the latest release of Firefox does not list visitor groups when in edit-mode. When working inside a XHTML property, selecting some content, and hitting the green Visitor groups -button I am not seeing any items in the list after clicking the green "+" button.
Does anyone have a fix or workaround for this?