Here is the FireBug console error message I get when going to the email accounts page
Code:
uncaught exception: [Exception... "Security error" code: "1000" nsresult: "0x805303e8 (NS_ERROR_DOM_SECURITY_ERR)" location: "http://cpanel.********.com/cPanel_magic_revision_1309940073/cjt/cpanel-all-min.js Line: 17"]
http://cpanel.********.com/cPanel_magic_revision_1306916064/editarea/edit_area/edit_area_full.js
Line 12
Note that this is after I have disabled some of the custom js I had added which does some Cufon stuff and I can do without. I figured if we can get the cpanel pages working again first, then I look again at making everything look pretty 
Further, I still get the same error if I disable all additional javascript leaving only the original x3 javascript originally in the template.
FYI ... I created our branding simply by taking a copy of x3 and adding additional HTML into the headers/footer to provide our header/sidebar/footer and left all 'cpanel content' areas intact. I removed no cpanel code from the templates. (or at least I believe I didn't)