For those of you using TinyMCE in your Joomla 1.0.x install, you may find that there's an error that occurs when you're trying to create a link or add an image.  Basically, the issue presents itself when TinyMCE needs to load a popup window, and it manifests itself by showing a blank window and issuing the following error:

uncaught exception: Permission denied to get property Window.tinyMCE

 ...followed by a couple of complaints stating:

tinyMCE has no properties

This problem is caused by the TinyMCE javascript files residing in a different domain or subdomain than the admin site.  If you want to know why it occurs, Mozilla discusses it under the topic, Same Origin Policy.  Their fix is to enter:

document.domain = "domain.com";

... which would be implemented by editing the tiny_mce_popup.js file (inside the TinyMCE folder) and adding the line at the top of the init block -- so that it's the first line inside init.

In the case of our Joomla install, this did not work and we ended up with a different error... because the issue had to do with the live site variable inside configuration.php.  We recommend, therefore, not editing tiny_mce_popup.js, but rather editing your configuration.php file to show 'www' in your $mosConfig_live_site variable.  Like so:

$mosConfig_live_site = 'http://www.yoursite.com';

It worked for us, and we hope that it works for you!