--- a/mail/components/extensions/parent/ext-mail.js
+++ b/mail/components/extensions/parent/ext-mail.js
@@ -1495,18 +1495,23 @@ var messageListTracker = {
   },
 
   _getNextPage(messageList) {
     let messageCount = Services.prefs.getIntPref(
       "extensions.webextensions.messagesPerPage",
       100
     );
     let page = [];
-    for (let i = 0; i < messageCount && messageList.hasMoreElements(); i++) {
-      page.push(messageList.getNext().QueryInterface(Ci.nsIMsgDBHdr));
+    let i = 0;
+    while (i < messageCount && messageList.hasMoreElements()) {
+      let next = messageList.getNext();
+      if (next) {
+        page.push(next.QueryInterface(Ci.nsIMsgDBHdr));
+        i++;
+      }
     }
     return page;
   },
 };
 
 class MessageManager {
   constructor(extension) {
     this.extension = extension;

--- a/mail/components/extensions/parent/ext-messages.js
+++ b/mail/components/extensions/parent/ext-messages.js
@@ -192,17 +192,19 @@ this.messages = class extends ExtensionA
 
           let collectionArray = await new Promise(resolve => {
             query.getCollection({
               onItemsAdded(items, collection) {},
               onItemsModified(items, collection) {},
               onItemsRemoved(items, collection) {},
               onQueryCompleted(collection) {
                 resolve(
-                  collection.items.map(glodaMsg => glodaMsg.folderMessage)
+                  collection.items
+                    .map(glodaMsg => glodaMsg.folderMessage)
+                    .filter(Boolean)
                 );
               },
             });
           });
 
           if (queryInfo.unread !== null) {
             collectionArray = collectionArray.filter(
               msg => msg.isRead == !queryInfo.unread