--- a/browser/components/extensions/ext-tabs.js
+++ b/browser/components/extensions/ext-tabs.js
@@ -762,57 +762,61 @@ this.tabs = class extends ExtensionAPI {
 
         printPreview() {
           let activeTab = getTabOrActive(null);
           let {
             PrintUtils,
             PrintPreviewListener,
           } = activeTab.ownerGlobal;
 
-          return new Promise(resolve => {
+          return new Promise((resolve, reject) => {
             let ppBrowser = PrintUtils._shouldSimplify ?
               PrintPreviewListener.getSimplifiedPrintPreviewBrowser() :
               PrintPreviewListener.getPrintPreviewBrowser();
 
             let mm = ppBrowser.messageManager;
 
             let onEntered = (message) => {
               mm.removeMessageListener("Printing:Preview:Entered", onEntered);
               if (message.data.failed) {
-                throw new ExtensionError("Print preview failed");
+                reject({message: "Print preview failed"});
               }
               resolve();
             };
 
             mm.addMessageListener("Printing:Preview:Entered", onEntered);
 
             PrintUtils.printPreview(PrintPreviewListener);
           });
         },
 
         saveAsPDF(pageSettings) {
           let activeTab = getTabOrActive(null);
           let picker = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
           let title = strBundle.GetStringFromName("saveaspdf.saveasdialog.title");
 
+          if (AppConstants.platform === "macosx") {
+            return Promise.reject({message: "Not supported on Mac OS X"});
+          }
+
           picker.init(activeTab.ownerGlobal, title, Ci.nsIFilePicker.modeSave);
           picker.appendFilter("PDF", "*.pdf");
           picker.defaultExtension = "pdf";
           picker.defaultString = activeTab.linkedBrowser.contentTitle + ".pdf";
 
           return new Promise(resolve => {
             picker.open(function(retval) {
               if (retval == 0 || retval == 2) {
                 // OK clicked (retval == 0) or replace confirmed (retval == 2)
                 try {
                   let fstream = Cc["@mozilla.org/network/file-output-stream;1"].createInstance(Ci.nsIFileOutputStream);
                   fstream.init(picker.file, 0x2A, 0x1B6, 0);  // write|create|truncate, file permissions rw-rw-rw- = 0666 = 0x1B6
                   fstream.close();  // unlock file
                 } catch (e) {
-                  resolve(retval == 0 ? "Not saved" : "Not replaced");
+                  resolve(retval == 0 ? "not_saved" : "not_replaced");
                   return;
                 }
 
                 let psService = Cc["@mozilla.org/gfx/printsettings-service;1"].getService(Ci.nsIPrintSettingsService);
                 let printSettings = psService.newPrintSettings;
 
                 printSettings.printToFile = true;
                 printSettings.toFileName = picker.file.path;
@@ -875,20 +879,20 @@ this.tabs = class extends ExtensionAPI {
                   printSettings.marginTop = pageSettings.marginTop;
                 }
                 if (pageSettings.marginBottom !== null) {
                   printSettings.marginBottom = pageSettings.marginBottom;
                 }
 
                 activeTab.linkedBrowser.print(activeTab.linkedBrowser.outerWindowID, printSettings, null);
 
-                resolve(retval == 0 ? "Saved" : "Replaced");
+                resolve(retval == 0 ? "saved" : "replaced");
               } else {
                 // Cancel clicked (retval == 1)
-                resolve("Cancelled");
+                resolve("canceled");
               }
             });
           });
         },
       },
     };
     return self;
   }

--- a/browser/components/extensions/schemas/tabs.json
+++ b/browser/components/extensions/schemas/tabs.json
@@ -1150,17 +1150,17 @@
             "type": "function",
             "name": "callback",
             "optional": true,
             "description": "Called after save as dialog closed.",
             "parameters": [
               {
                 "type": "string",
                 "name": "status",
-                "description": "Save status: Saved, Replaced, Cancelled, Not Saved, Not Replaced."
+                "description": "Save status: saved, replaced, canceled, not_saved, not_replaced."
               }
             ]
           }
         ]
       }
     ],
     "events": [
       {