Stop Firefox from jumping when widget div is displayed. Issue 186.

core/widgetdiv.js

@@ -30,6 +30,7 @@ goog.provide('Blockly.WidgetDiv');
 
 goog.require('Blockly.Css');
 goog.require('goog.dom');
+goog.require('goog.style');
 
 
 /**
@@ -75,6 +76,10 @@ Blockly.WidgetDiv.show = function(newOwner, rtl, dispose) {
   Blockly.WidgetDiv.hide();
   Blockly.WidgetDiv.owner_ = newOwner;
   Blockly.WidgetDiv.dispose_ = dispose;
+  // Temporarily move the widget to the top of the screen so that it does not
+  // cause a scrollbar jump in Firefox when displayed.
+  var xy = goog.style.getViewportPageOffset(document);
+  Blockly.WidgetDiv.DIV.style.top = xy.y + 'px';
   Blockly.WidgetDiv.DIV.style.direction = rtl ? 'rtl' : 'ltr';
   Blockly.WidgetDiv.DIV.style.display = 'block';
 };

tests/playground.html

@@ -87,8 +87,8 @@ function start() {
              {enabled: true,
               controls: true,
               wheel: true,
-              maxScale: 2,
-              minScale: .1,
+              maxScale: 4,
+              minScale: .25,
               scaleSpeed: 1.1
              },
           });