Allow option to disable entirely for non-supported browsers

I need to follow up with a more complete description, but the short form is thus:

On unsupported or partially supported browsers (e.g. Safari), if the settings are such that TinyMCE is enabled everywhere by default, the site is very hard to use for anonymous users.

The best suggestion I've seen is to disable TinyMCE for all unsupported browsers and have a small note underneath text areas saying something like "Your browser is unsupported for rich text editing. Consider using Firefox if you would like rich text editing". This functionality should be configurable as should be the message.