MP3 player not shown when use external YUI enabled

1. Enable the site setting 'useexternalyui'
2. Enable the Multimedia filter (and mark the 'filter_mediaplugin_enable_mp3' checkbox if the option is available in your moodle version, otherwise is enabled)
3. Add a link to a MP3 file (one of the user private files for example) in any HTML text area
4. View the page with the HTML text displayed, the link SHOULD BE replaced by the MP3 player and there SHOULD NOT BE a JS error

Access to the style sheets wrapped in a try & catch. This solution does not replicate the same exact funcionality with 'useexternalyui' enabled, but I'm afraid that it's not possible, is a JS security restriction.

Solution tested on Firefox, Chrome and Opera; IE is, as always, another world, it doesn't replace the player with 'userexternalyui' enabled nor disabled, but it seems that there is no security violation when accessing cross domain style sheets, since it's another issue I think that you prefer to have it on another tracker issue.

Grepping around moodle core code to find more 'document.styleSheets' to prevent other JS security violations when online YUI libraries is enabled, it seems that this is the only place where the styles sheets are accessed this way; the other apperance is in the jquery lib of xhprof which I suppose is stand-alone and not dependent of the moodle core YUI libraries.