--- a/content/html/document/src/nsHTMLDocument.cpp
+++ b/content/html/document/src/nsHTMLDocument.cpp
@@ -2948,17 +2948,19 @@ ConvertToMidasInternalCommandInner(const
             for (j = 0; j < ArrayLength(gBlocks); ++j) {
               if (convertedParam.Equals(gBlocks[j],
                                         nsCaseInsensitiveCStringComparator())) {
                 outParam.Assign(gBlocks[j]);
                 break;
               }
             }
 
-            return j != ArrayLength(gBlocks);
+            if (j == ArrayLength(gBlocks)) {
+              outParam.Truncate();
+            }
           }
           else {
             CopyUTF16toUTF8(inParam, outParam);
           }
         }
       }
     }
   } // end else for useNewParam (do convert existing param)
@@ -3096,16 +3098,21 @@ nsHTMLDocument::ExecCommand(const nsAStr
     return NS_ERROR_FAILURE;
 
   nsCAutoString cmdToDispatch, paramStr;
   bool isBool, boolVal;
   if (!ConvertToMidasInternalCommand(commandID, value,
                                      cmdToDispatch, paramStr, isBool, boolVal))
     return NS_OK;
 
+  if (cmdToDispatch.EqualsLiteral("cmd_paragraphState") && paramStr.IsEmpty()) {
+    // Invalid value
+    return NS_OK;
+  }
+
   if (!isBool && paramStr.IsEmpty()) {
     rv = cmdMgr->DoCommand(cmdToDispatch.get(), nsnull, window);
   } else {
     // we have a command that requires a parameter, create params
     nsCOMPtr<nsICommandParams> cmdParams = do_CreateInstance(
                                             NS_COMMAND_PARAMS_CONTRACTID, &rv);
     if (!cmdParams)
       return NS_ERROR_OUT_OF_MEMORY;
@@ -3174,20 +3181,18 @@ nsHTMLDocument::QueryCommandIndeterm(con
   GetMidasCommandManager(getter_AddRefs(cmdMgr));
   if (!cmdMgr)
     return NS_ERROR_FAILURE;
 
   nsIDOMWindow *window = GetWindow();
   if (!window)
     return NS_ERROR_FAILURE;
 
-  nsCAutoString cmdToDispatch, paramToCheck;
-  bool dummy;
-  if (!ConvertToMidasInternalCommand(commandID, commandID,
-                                     cmdToDispatch, paramToCheck, dummy, dummy))
+  nsCAutoString cmdToDispatch;
+  if (!ConvertToMidasInternalCommand(commandID, cmdToDispatch))
     return NS_ERROR_NOT_IMPLEMENTED;
 
   nsresult rv;
   nsCOMPtr<nsICommandParams> cmdParams = do_CreateInstance(
                                            NS_COMMAND_PARAMS_CONTRACTID, &rv);
   NS_ENSURE_SUCCESS(rv, rv);
 
   rv = cmdMgr->GetCommandState(cmdToDispatch.get(), window, cmdParams);