Issue 6496 - Account for browsers that don't support notifications with buttons

lib/subscriptionInit.js

Index: lib/subscriptionInit.js
===================================================================
--- a/lib/subscriptionInit.js
+++ b/lib/subscriptionInit.js
@@ -133,6 +133,31 @@
   return selectedItem;
 }
 
+function supportsNotificationsWithButtons()
+{
+  // Microsoft Edge (as of EdgeHTML 16) doesn't have the notifications API.
+  // Opera gives an asynchronous error when buttons are provided (we cannot
+  // detect that behavior without attempting to show a notification).
+  if (!("notifications" in browser) || info.application == "opera")
+    return false;
+
+  // Firefox throws synchronously if the "buttons" option is provided.
+  // If buttons are supported (i.e. on Chrome), this fails with
+  // a different error message due to missing required options.
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1190681
+  try
+  {
+    browser.notifications.create({buttons: []});
+  }
+  catch (e)
+  {
+    if (e.toString().includes('"buttons" is unsupported'))
+      return false;
+  }
+
+  return true;
+}
+
 /**
  * Gets the filter subscriptions to be added when the extnesion is loaded.
  *
@@ -155,11 +180,16 @@
     acceptableAdsSubscription.title = "Allow non-intrusive advertising";
     subscriptions.push(acceptableAdsSubscription);
 
-    let antiAdblockSubscription = Subscription.fromURL(
-      Prefs.subscriptions_antiadblockurl
-    );
-    antiAdblockSubscription.disabled = true;
-    subscriptions.push(antiAdblockSubscription);
+    // Only add the anti-adblock messages subscription if
+    // the related notification can be shown on this browser.
+    if (supportsNotificationsWithButtons())
+    {
+      let antiAdblockSubscription = Subscription.fromURL(
+        Prefs.subscriptions_antiadblockurl
+      );
+      antiAdblockSubscription.disabled = true;
+      subscriptions.push(antiAdblockSubscription);
+    }
   }
 
   // Add default ad blocking subscription (e.g. EasyList)