It seems that upgrading tinyMCE to latest version fixes the problems in IE9.
http://www.tinymce.com/download/download.php
Download latest 3.4.7 version and replace the old files on your FTP (don't forget to backup the old one).
You don't need to upload all plug-ins, just following ones:
- advimage
- fullscreen
- inlinepopups
- media
After overwriting files, clean your browser cache, refresh your page and WYSIWIG editor should fully work in your browser.
Regarding the FF/Chrome/Safari/IE or Opera debate, well everybody have the right to choose their own preferred apps.
As for me, I would burn IE in eternal flames of hell (no matter the version) never to be released again