--- a/mobile/android/chrome/content/browser.js
+++ b/mobile/android/chrome/content/browser.js
@@ -3817,16 +3817,20 @@ Tab.prototype = {
       aMetadata.defaultZoom *= scaleRatio;
     if (aMetadata.minZoom > 0)
       aMetadata.minZoom *= scaleRatio;
     if (aMetadata.maxZoom > 0)
       aMetadata.maxZoom *= scaleRatio;
 
     aMetadata.isRTL = this.browser.contentDocument.documentElement.dir == "rtl";
 
+    // if the metadata hasn't actually changed, no need to do anything
+    if (aMetadata.equals(this.metadata))
+      return;
+
     ViewportHandler.setMetadataForDocument(this.browser.contentDocument, aMetadata);
     this.updateViewportSize(gScreenWidth, aInitialLoad);
     this.sendViewportMetadata();
   },
 
   /** Update viewport when the metadata or the window size changes. */
   updateViewportSize: function updateViewportSize(aOldScreenWidth, aInitialLoad) {
     // When this function gets called on window resize, we must execute
@@ -5803,16 +5807,28 @@ ViewportMetadata.prototype = {
   height: null,
   defaultZoom: null,
   minZoom: null,
   maxZoom: null,
   autoSize: null,
   allowZoom: null,
   isSpecified: null,
   isRTL: null,
+
+  equals: function(aOther) {
+    return this.width === aOther.width
+        && this.height === aOther.height
+        && this.defaultZoom === aOther.defaultZoom
+        && (this.minZoom === aOther.minZoom || (isNaN(minZoom) && isNaN(aOther.minZoom)))
+        && (this.maxZoom === aOther.maxZoom || (isNaN(maxZoom) && isNaN(aOther.maxZoom)))
+        && this.autoSize === aOther.autoSize
+        && this.allowZoom === aOther.allowZoom
+        && this.isSpecified === aOther.isSpecified
+        && this.isRTL === aOther.isRTL;
+  }
 };
 
 
 /**
  * Handler for blocked popups, triggered by DOMUpdatePageReport events in browser.xml
  */
 var PopupBlockerObserver = {
   onUpdatePageReport: function onUpdatePageReport(aEvent) {