--- a/toolkit/modules/RemoteController.jsm
+++ b/toolkit/modules/RemoteController.jsm
@@ -43,24 +43,25 @@ RemoteController.prototype = {
 
   doCommandWithParams: function(aCommand, aCommandParams) {
     let cmd = {
       cmd: aCommand,
       params: null
     };
     if (aCommand == "cmd_lookUpDictionary") {
       let rect = this._browser.getBoundingClientRect();
+      let scale = this._browser.ownerDocument.defaultView.devicePixelRatio;
       cmd.params = {
         x:  {
           type: "long",
-          value: aCommandParams.getLongValue("x") - rect.left
+          value: aCommandParams.getLongValue("x") - rect.left * scale
         },
         y: {
           type: "long",
-          value: aCommandParams.getLongValue("y") - rect.top
+          value: aCommandParams.getLongValue("y") - rect.top * scale
         }
       };
     } else {
       throw Cr.NS_ERROR_NOT_IMPLEMENTED;
     }
     this._browser.messageManager.sendAsyncMessage(
       "ControllerCommands:DoWithParams", cmd);
   },