diff --git a/core/events.js b/core/events.js
index 12766f220..b117b4eda 100644
--- a/core/events.js
+++ b/core/events.js
@@ -90,6 +90,13 @@ Blockly.Events.UI = 'ui';
  */
 Blockly.Events.FIRE_QUEUE_ = [];
 
+/**
+ * Pending timeout, if any, for event firing.
+ * @type {?number}
+ * @private
+ */
+Blockly.Events.FIRE_TIMER_ = undefined;
+
 /**
  * Create a custom event and fire it.
  * @param {!Blockly.Events.Abstract} event Custom data for event.
@@ -98,11 +105,14 @@ Blockly.Events.fire = function(event) {
   if (!Blockly.Events.isEnabled()) {
     return;
   }
-  if (!Blockly.Events.FIRE_QUEUE_.length) {
-    // First event added; schedule a firing of the event queue.
-    setTimeout(Blockly.Events.fireNow_, 0);
-  }
   Blockly.Events.FIRE_QUEUE_.push(event);
+  if (!Blockly.Events.FIRE_TIMER_) {
+    // First event added; schedule a firing of the event queue.
+    Blockly.Events.FIRE_TIMER_ = setTimeout(function() {
+      Blockly.Events.FIRE_TIMER_ = undefined;
+      Blockly.Events.fireNow_();
+    });
+  }
 };
 
 /**
diff --git a/core/mutator.js b/core/mutator.js
index 6881c5dce..f241b305f 100644
--- a/core/mutator.js
+++ b/core/mutator.js
@@ -171,6 +171,16 @@ Blockly.Mutator.prototype.updateEditable = function() {
   Blockly.Icon.prototype.updateEditable.call(this);
 };
 
+Blockly.Mutator.prototype.scheduleResizeBubble = function() {
+  if (!this.pendingBubbleResize_) {
+    var self = this;
+    this.pendingBubbleResize_ = setTimeout(function() {
+      self.workspace_ && self.resizeBubble_();
+      self.pendingBubbleResize_ = undefined;
+    });
+  }
+}
+
 /**
  * Callback function triggered when the bubble has resized.
  * Resize the workspace accordingly.
@@ -224,6 +234,8 @@ Blockly.Mutator.prototype.setVisible = function(visible) {
   Blockly.Events.fire(
       new Blockly.Events.Ui(this.block_, 'mutatorOpen', !visible, visible));
   if (visible) {
+    Blockly.Field.startCache();
+    Blockly.Events.disable();
     // Create the bubble.
     this.bubble_ = new Blockly.Bubble(
         /** @type {!Blockly.WorkspaceSvg} */ (this.block_.workspace),
@@ -235,10 +247,7 @@ Blockly.Mutator.prototype.setVisible = function(visible) {
     }
 
     this.rootBlock_ = this.block_.decompose(this.workspace_);
-    var blocks = this.rootBlock_.getDescendants();
-    for (var i = 0, child; child = blocks[i]; i++) {
-      child.render();
-    }
+    this.renderWorkspace();
     // The root block should not be dragable or deletable.
     this.rootBlock_.setMovable(false);
     this.rootBlock_.setDeletable(false);
@@ -266,6 +275,8 @@ Blockly.Mutator.prototype.setVisible = function(visible) {
     // When the mutator's workspace changes, update the source block.
     this.workspace_.addChangeListener(this.workspaceChanged_.bind(this));
     this.updateColour();
+    Blockly.Events.enable();
+    Blockly.Field.stopCache();
   } else {
     // Dispose of the bubble.
     this.svgDialog_ = null;
@@ -283,6 +294,16 @@ Blockly.Mutator.prototype.setVisible = function(visible) {
   }
 };
 
+/**
+ * Renders the mutator's workspace, starting from the root block.
+ */
+Blockly.Mutator.prototype.renderWorkspace = function() {
+  var blocks = this.rootBlock_.getDescendants();
+  for (var i = 0, child; child = blocks[i]; i++) {
+    child.render();
+  }
+};
+
 /**
  * Update the source block when the mutator's blocks are changed.
  * Bump down any block that's too high.
@@ -305,6 +326,7 @@ Blockly.Mutator.prototype.workspaceChanged_ = function() {
 
   // When the mutator's workspace changes, update the source block.
   if (this.rootBlock_.workspace == this.workspace_) {
+    Blockly.Field.startCache();
     Blockly.Events.setGroup(true);
     var block = this.block_;
     var oldMutationDom = block.mutationToDom();
@@ -334,8 +356,9 @@ Blockly.Mutator.prototype.workspaceChanged_ = function() {
     if (block.rendered) {
       block.render();
     }
-    this.resizeBubble_();
+    this.scheduleResizeBubble();
     Blockly.Events.setGroup(false);
+    Blockly.Field.stopCache();
   }
 };
 
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index 96cb15128..a5da8f59b 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -521,16 +521,19 @@ Blockly.WorkspaceSvg.prototype.updateScreenCalculations_ = function() {
  * @package
  */
 Blockly.WorkspaceSvg.prototype.resizeContents = function() {
-  if (!this.resizesEnabled_ || !this.rendered) {
+  if (!this.resizesEnabled_ || !this.rendered || this.pendingResize_) {
     return;
   }
-  if (this.scrollbar) {
-    // TODO(picklesrus): Once rachel-fenichel's scrollbar refactoring
-    // is complete, call the method that only resizes scrollbar
-    // based on contents.
-    this.scrollbar.resize();
-  }
-  this.updateInverseScreenCTM();
+  this.pendingResize_ = setTimeout((function() {
+    if (this.scrollbar) {
+      // TODO(picklesrus): Once rachel-fenichel's scrollbar refactoring
+      // is complete, call the method that only resizes scrollbar
+      // based on contents.
+      this.scrollbar.resize();
+    }
+    this.updateInverseScreenCTM();
+    this.pendingResize_ = undefined;
+  }).bind(this));
 };
 
 /**