In Firefox (only), clicking on the tinyMCE image editor in either a post or a page causes this series of errors (immediately):
uncaught exception: Permission denied to get property Window.tinyMCE
uncaught exception: Permission denied to get property Window.addEventListener
tinyMCE has no properties
I cannot find any in the wp forums on this, and only something via Google on cross-site scripting. I'm doing everything under a single domain, so I haven't been able to figure out how that might be a factor.
This works fine in IE, just not in Firefox.