there are two tabs in the speech window, speech recognition is the one you are referring too, the other is text to speech, that's the one me thinks... It might be different if you are running leopard. I tried to simulate your problem myself, couldn't do it, I'm running tiger.
The bookmark thing, either, control+click the bookmark > delete (actually, this only works for the bookmarks in the toolbar of the browers window) or in the Firefox toolbar under bookmarks > organize bookmarks.