If you are using tinymce across subdomains you need to uncomment and changedocument.domain in tiny_mce_popup.js.

fix-tinymce-popup.sh

# document.domain is commented by default, change it to our domain and uncomment it, this will edit file in place
sed -i "s/\/\/ document.domain = 'moxiecode.com';/document.domain = 'example.com';/" path/to/tiny_mce/tiny_mce_popup.js

# note that in order to get this working on os x, you must pass argument to -i
# this will save unedited copy of tiny_mce_popup.js as tiny_mce_popup.js.tmp
sed -i ".tmp" "s/\/\/ document.domain = 'moxiecode.com';/document.domain = 'example.com';/" path/to/tiny_mce/tiny_mce_popup.js