diff --git a/content/base/public/nsIDocument.h b/content/base/public/nsIDocument.h
index 7e3a3c68fbb4..b1f5a7565a56 100644
--- a/content/base/public/nsIDocument.h
+++ b/content/base/public/nsIDocument.h
@@ -1600,6 +1600,8 @@ public:
   void WarnOnceAbout(DeprecatedOperations aOperation);
 
   virtual void PostVisibilityUpdateEvent() = 0;
+  
+  bool IsSyntheticDocument() { return mIsSyntheticDocument; }
 
   void SetNeedLayoutFlush() {
     mNeedLayoutFlush = true;
diff --git a/content/events/src/nsEventStateManager.cpp b/content/events/src/nsEventStateManager.cpp
index af114c5b5fe9..bbf065e79240 100644
--- a/content/events/src/nsEventStateManager.cpp
+++ b/content/events/src/nsEventStateManager.cpp
@@ -2516,7 +2516,7 @@ nsEventStateManager::DoScrollZoom(nsIFrame *aTargetFrame,
       // positive adjustment to decrease zoom, negative to increase
       PRInt32 change = (adjustment > 0) ? -1 : 1;
 
-      if (Preferences::GetBool("browser.zoom.full")) {
+      if (Preferences::GetBool("browser.zoom.full") || content->GetCurrentDoc()->IsSyntheticDocument()) {
         ChangeFullZoom(change);
       } else {
         ChangeTextSize(change);
diff --git a/toolkit/content/viewZoomOverlay.js b/toolkit/content/viewZoomOverlay.js
index f95c5458f8a5..9f2bc945d8c2 100644
--- a/toolkit/content/viewZoomOverlay.js
+++ b/toolkit/content/viewZoomOverlay.js
@@ -79,8 +79,9 @@ var ZoomManager = {
   getZoomForBrowser: function ZoomManager_getZoomForBrowser(aBrowser) {
     var markupDocumentViewer = aBrowser.markupDocumentViewer;
 
-    return this.useFullZoom ? markupDocumentViewer.fullZoom
-                            : markupDocumentViewer.textZoom;
+    return this.useFullZoom || 
+      aBrowser.contentDocument.mozSyntheticDocument ?
+      markupDocumentViewer.fullZoom : markupDocumentViewer.textZoom;
   },
 
   set zoom(aVal) {
@@ -94,7 +95,7 @@ var ZoomManager = {
 
     var markupDocumentViewer = aBrowser.markupDocumentViewer;
 
-    if (this.useFullZoom) {
+    if (this.useFullZoom || aBrowser.contentDocument.mozSyntheticDocument) {
       markupDocumentViewer.textZoom = 1;
       markupDocumentViewer.fullZoom = aVal;
     } else {