After installing / uninstalling / installing, calling Adobe, deleting preferences ... in short, a great deal of wasting time (that I do not want you to do) ... the problem is somewhere else.
I've read the solution on a post (but too much posts read and I do not remember which one) :
That's it, and everything's now back to normal.
Hope it will help...
Thanks for sharing!
This Adobe Help page suggests uninstalling the Flashbug/FlashFirebug plug-in for Firefox if there's a problem with blank panels within Fireworks, particularly on the Windows OS. It's good to know that the same advice can help Mac users, too.