I don't think it's a Firefox problem. "wyciwyg" just means that that blank page was generated by a script (and firefox caches those pages with the "wyciwyg://" URI-prefix).
I have the same problem, but with the e-mail cloaker plugin from joomla 1.7.
I am guessing there is a common ground here and wondering about a common script error (jquery or mootools or ...) ??
Anyway, if anyone has more info on this, pleas notify us.
Here is my problem topic:
forum.joomla.org/viewtopic.php?p=2711495#p2711495