diff --git a/extensions/firefox/content/PdfStreamConverter.jsm b/extensions/firefox/content/PdfStreamConverter.jsm
index 9e12f10f2..d21d4b2d9 100644
--- a/extensions/firefox/content/PdfStreamConverter.jsm
+++ b/extensions/firefox/content/PdfStreamConverter.jsm
@@ -423,6 +423,12 @@ ChromeActions.prototype = {
     }
     return true;
   },
+  supportedMouseWheelZoomModifierKeys: function() {
+    return {
+      ctrlKey: getIntPref('mousewheel.with_control.action', 3) === 3,
+      metaKey: getIntPref('mousewheel.with_meta.action', 1) === 3,
+    };
+  },
   reportTelemetry: function (data) {
     var probeInfo = JSON.parse(data);
     switch (probeInfo.type) {
@@ -827,7 +833,7 @@ RequestListener.prototype.receive = function(event) {
   var response;
   if (sync) {
     response = actions[action].call(this.actions, data);
-    event.detail.response = response;
+    event.detail.response = makeContentReadable(response, doc.defaultView);
   } else {
     if (!event.detail.responseExpected) {
       doc.documentElement.removeChild(message);
diff --git a/web/viewer.js b/web/viewer.js
index d14cc50b7..bbe1f6696 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -401,6 +401,18 @@ var PDFViewerApplication = {
     return PDFJS.shadow(this, 'loadingBar', bar);
   },
 
+  get supportedMouseWheelZoomModifierKeys() {
+    var support = {
+      ctrlKey: true,
+      metaKey: true,
+    };
+//#if (FIREFOX || MOZCENTRAL)
+//  support = FirefoxCom.requestSync('supportedMouseWheelZoomModifierKeys');
+//#endif
+
+    return PDFJS.shadow(this, 'supportedMouseWheelZoomModifierKeys', support);
+  },
+
 //#if (FIREFOX || MOZCENTRAL)
   initPassiveLoading: function pdfViewInitPassiveLoading() {
     function FirefoxComDataRangeTransport(length, initialData) {
@@ -1898,6 +1910,11 @@ function handleMouseWheel(evt) {
     PDFViewerApplication.scrollPresentationMode(ticks *
                                                 MOUSE_WHEEL_DELTA_FACTOR);
   } else if (evt.ctrlKey || evt.metaKey) {
+    var support = PDFViewerApplication.supportedMouseWheelZoomModifierKeys;
+    if ((evt.ctrlKey && !support.ctrlKey) ||
+        (evt.metaKey && !support.metaKey)) {
+      return;
+    }
     // Only zoom the pages, not the entire viewer.
     evt.preventDefault();