You might have encountered this issue if you are still using an older version of TinyMCE. Older versions of TinyMCE are not showing the content inside the editor in FireFox 11. The editor is working fine in FF10.x. I’m not sure exactly which versions of TinyMCE has this issue. This is the case if you are still using earlier minor versions of Joomla 1.5 for your website. The TinyMCE version comes with Joomla 1.5 early versions does not work properly in FireFox 11.
I wish you the best with that 😉
Please share your experience in comments section below.