I use QuickTextPaste from softwareok.com, Firefox 17 and 17.0.1 don't allow pasting. 16.X does is there a work around besides not using QuickTextPaste.
Try to set the Boolean pref dom.event.clipboardevents.enabled to false on the about:config page.
I'm trying to work around this with another product to manage preset text strings with hotkeys. Maybe Ditto? Suggestions? I contacted SoftwareOK.com too.
I tried using AllowClipboardHelper with FF v 18.0.1 if didn't work. I have the same problem with the last 2 versions of SeaMonkey.
I haven't tried allowing Java scripts access clipboard.