call preventdefault for keypresses we insert (r=akkana, sr=sfraser) bug 158672 (and others)

editor/libeditor/text/nsPlaintextEditor.cpp

@@ -527,6 +527,7 @@ NS_IMETHODIMP nsPlaintextEditor::HandleKeyPress(nsIDOMKeyEvent* aKeyEvent)
     
     if (character && !altKey && !ctrlKey && !isShift && !metaKey)
     {
+      aKeyEvent->PreventDefault();
       nsAutoString key(character);
       return TypedText(key, eTypedText);
     }