--- a/browser/base/content/content.js
+++ b/browser/base/content/content.js
@@ -41,16 +41,18 @@ XPCOMUtils.defineLazyModuleGetter(this, 
 XPCOMUtils.defineLazyGetter(this, "PageMenuChild", function() {
   let tmp = {};
   Cu.import("resource://gre/modules/PageMenu.jsm", tmp);
   return new tmp.PageMenuChild();
 });
 XPCOMUtils.defineLazyModuleGetter(this, "Feeds",
   "resource:///modules/Feeds.jsm");
 
+Cu.importGlobalProperties(["URL"]);
+
 // TabChildGlobal
 var global = this;
 
 // Load the form validation popup handler
 var formSubmitObserver = new FormSubmitObserver(content, this);
 
 addMessageListener("ContextMenu:DoCustomCommand", function(message) {
   E10SUtils.wrapHandlingUserInput(
@@ -787,19 +789,21 @@ addMessageListener("ContextMenu:MediaCom
       break;
     case "fullscreen":
       if (content.document.fullscreenEnabled)
         media.requestFullscreen();
       break;
   }
 });
 
-addMessageListener("ContextMenu:Canvas:ToDataURL", (message) => {
-  let dataURL = message.objects.target.toDataURL();
-  sendAsyncMessage("ContextMenu:Canvas:ToDataURL:Result", { dataURL });
+addMessageListener("ContextMenu:Canvas:ToBlobURL", (message) => {
+  message.objects.target.toBlob((blob) => {
+    let blobURL = URL.createObjectURL(blob);
+    sendAsyncMessage("ContextMenu:Canvas:ToBlobURL:Result", { blobURL });
+  });
 });
 
 addMessageListener("ContextMenu:ReloadFrame", (message) => {
   message.objects.target.ownerDocument.location.reload();
 });
 
 addMessageListener("ContextMenu:ReloadImage", (message) => {
   let image = message.objects.target;

--- a/browser/base/content/nsContextMenu.js
+++ b/browser/base/content/nsContextMenu.js
@@ -1135,35 +1135,35 @@ nsContextMenu.prototype = {
     urlSecurityCheck(this.mediaURL,
                      this.browser.contentPrincipal,
                      Ci.nsIScriptSecurityManager.DISALLOW_SCRIPT);
 
     this.browser.messageManager.sendAsyncMessage("ContextMenu:ReloadImage",
                                                  null, { target: this.target });
   },
 
-  _canvasToDataURL: function(target) {
+  _canvasToBlobURL: function(target) {
     let mm = this.browser.messageManager;
     return new Promise(function(resolve) {
-      mm.sendAsyncMessage("ContextMenu:Canvas:ToDataURL", {}, { target });
+      mm.sendAsyncMessage("ContextMenu:Canvas:ToBlobURL", {}, { target });
 
       let onMessage = (message) => {
-        mm.removeMessageListener("ContextMenu:Canvas:ToDataURL:Result", onMessage);
-        resolve(message.data.dataURL);
+        mm.removeMessageListener("ContextMenu:Canvas:ToBlobURL:Result", onMessage);
+        resolve(message.data.blobURL);
       };
-      mm.addMessageListener("ContextMenu:Canvas:ToDataURL:Result", onMessage);
+      mm.addMessageListener("ContextMenu:Canvas:ToBlobURL:Result", onMessage);
     });
   },
 
   // Change current window to the URL of the image, video, or audio.
   viewMedia: function(e) {
     let referrerURI = gContextMenuContentData.documentURIObject;
     if (this.onCanvas) {
-      this._canvasToDataURL(this.target).then(function(dataURL) {
-        openUILink(dataURL, e, { disallowInheritPrincipal: true,
+      this._canvasToBlobURL(this.target).then(function(blobURL) {
+        openUILink(blobURL, e, { disallowInheritPrincipal: true,
                                  referrerURI: referrerURI });
       }, Cu.reportError);
     }
     else {
       urlSecurityCheck(this.mediaURL,
                        this.browser.contentPrincipal,
                        Ci.nsIScriptSecurityManager.DISALLOW_SCRIPT);
       openUILink(this.mediaURL, e, { disallowInheritPrincipal: true,
@@ -1430,18 +1430,18 @@ nsContextMenu.prototype = {
 
   // Save URL of the clicked upon image, video, or audio.
   saveMedia: function() {
     let doc = this.ownerDoc;
     let referrerURI = gContextMenuContentData.documentURIObject;
     let isPrivate = PrivateBrowsingUtils.isBrowserPrivate(this.browser);
     if (this.onCanvas) {
       // Bypass cache, since it's a data: URL.
-      this._canvasToDataURL(this.target).then(function(dataURL) {
-        saveImageURL(dataURL, "canvas.png", "SaveImageTitle",
+      this._canvasToBlobURL(this.target).then(function(blobURL) {
+        saveImageURL(blobURL, "canvas.png", "SaveImageTitle",
                      true, false, referrerURI, null, null, null,
                      isPrivate);
       }, Cu.reportError);
     }
     else if (this.onImage) {
       urlSecurityCheck(this.mediaURL, this.principal);
       saveImageURL(this.mediaURL, null, "SaveImageTitle", false,
                    false, referrerURI, null, gContextMenuContentData.contentType,