Issue 4978 - Avoid custom filters from being displayed multiple times

options.js

Index: options.js
diff --git a/options.js b/options.js
index c7667b841390a2f15a95d295a48643c21dee7a33..25b18aa60d0f083d2bd04612cd1869607e39b6d0 100644
--- a/options.js
+++ b/options.js
@@ -92,6 +92,7 @@ const statusMessages = new Map([
 
 let delayedSubscriptionSelection = null;
 let acceptableAdsUrl;
+let specialSubscriptionBeingAdded = null;
 
 // Loads options from localStorage and sets UI elements accordingly
 function loadOptions()
@@ -193,6 +194,7 @@ $(loadOptions);
 
 function convertSpecialSubscription(subscription)
 {
+  specialSubscriptionBeingAdded = subscription.url;
   getFilters(subscription.url, filters =>
   {
     for (let filter of filters)
@@ -202,6 +204,7 @@ function convertSpecialSubscription(subscription)
       else
         appendToListBox("userFiltersBox", filter.text);
     }
+    specialSubscriptionBeingAdded = null;
   });
 }
 
@@ -503,8 +506,19 @@ function onPrefMessage(key, value)
     checkbox.checked = value;
 }
 
-function onFilterMessage(action, filter)
+function onFilterMessage(action, filter, subscription)
 {
+  // When the user adds a custom filter for the first time a special
+  // subscription is created automatically. When the happens we'll receive a
+  // message for the subscription first, then the filter. To avoid displaying
+  // the filter twice we have to be careful to ignore filter messages for a
+  // newly added subscription which we're still in the process of handling.
+  if (specialSubscriptionBeingAdded && subscription &&
+      subscription.url == specialSubscriptionBeingAdded)
+  {
+    return;
+  }
+
   switch (action)
   {
     case "loaded":
@@ -734,7 +748,7 @@ ext.onMessage.addListener(message =>
       }
       break;
     case "filters.respond":
-      onFilterMessage(message.action, message.args[0]);
+      onFilterMessage(message.action, message.args[0], message.args[1]);
       break;
     case "prefs.respond":
       onPrefMessage(message.action, message.args[0]);