diff --git a/mail/base/content/about3Pane.js b/mail/base/content/about3Pane.js
index 8fd7fc807f..3fc2ea2ceb 100644
--- a/mail/base/content/about3Pane.js
+++ b/mail/base/content/about3Pane.js
@@ -1234,17 +1234,7 @@ var folderPane = {
       }
 
       mode.containerList.replaceChildren();
-
-      if (typeof mode.init == "function") {
-        mode.init();
-      }
-      if (typeof mode.initServer == "function") {
-        for (let account of MailServices.accounts.accounts) {
-          if (account.incomingServer.type != "im") {
-            mode.initServer(account.incomingServer);
-          }
-        }
-      }
+      this._initMode(mode);
     }
     Services.xulStore.setValue(XULSTORE_URL, "folderTree", "compact", value);
   },
@@ -1282,17 +1272,38 @@ var folderPane = {
       `folderPaneModeHeader_${modeName}`
     );
     mode.containerList = container.querySelector("ul");
+    this._initMode(mode);
+    mode.active = true;
+  },
+
+  /**
+   * Initialize a folder mode with all visible accounts.
+   *
+   * @param {object} mode - One of the folder modes from `folderPane._modes`.
+   */
+  _initMode(mode) {
     if (typeof mode.init == "function") {
       mode.init();
     }
-    if (typeof mode.initServer == "function") {
-      for (let account of MailServices.accounts.accounts) {
-        if (account.incomingServer.type != "im") {
-          mode.initServer(account.incomingServer);
-        }
-      }
+    if (typeof mode.initServer != "function") {
+      return;
+    }
+
+    // `.accounts` is used here because it is ordered, `.allServers` isn't.
+    for (let account of MailServices.accounts.accounts) {
+      // Skip IM accounts.
+      if (account.incomingServer.type == "im") {
+        continue;
+      }
+      // Skip POP3 accounts that are deferred to another account.
+      if (
+        account.incomingServer instanceof Ci.nsIPop3IncomingServer &&
+        account.incomingServer.deferredToAccount
+      ) {
+        continue;
+      }
+      mode.initServer(account.incomingServer);
     }
-    mode.active = true;
   },
 
   /**
@@ -4016,32 +4027,42 @@ var folderListener = {
       threadTree.invalidate();
     }
   },
-  onFolderPropertyChanged(item, property, oldValue, newValue) {},
-  onFolderIntPropertyChanged(item, property, oldValue, newValue) {
+  onFolderPropertyChanged(folder, property, oldValue, newValue) {},
+  onFolderIntPropertyChanged(folder, property, oldValue, newValue) {
     switch (property) {
       case "BiffState":
         folderPane.changeNewMessages(
-          item,
+          folder,
           newValue === Ci.nsIMsgFolder.nsMsgBiffState_NewMail
         );
         break;
       case "FolderFlag":
-        folderPane.changeFolderFlag(item, oldValue, newValue);
+        folderPane.changeFolderFlag(folder, oldValue, newValue);
         break;
       case "TotalUnreadMessages":
-        folderPane.changeUnreadCount(item, oldValue, newValue);
+        folderPane.changeUnreadCount(folder, oldValue, newValue);
         break;
     }
   },
-  onFolderBoolPropertyChanged(item, property, oldValue, newValue) {
+  onFolderBoolPropertyChanged(folder, property, oldValue, newValue) {
     switch (property) {
+      case "isDeferred":
+        if (newValue) {
+          folderPane.removeFolder(null, folder);
+        } else {
+          folderPane.addFolder(null, folder);
+          for (let f of folder.descendants) {
+            folderPane.addFolder(f.parent, f);
+          }
+        }
+        break;
       case "NewMessages":
-        folderPane.changeNewMessages(item, newValue);
+        folderPane.changeNewMessages(folder, newValue);
         break;
     }
   },
-  onFolderUnicharPropertyChanged(item, property, oldValue, newValue) {},
-  onFolderPropertyFlagChanged(item, property, oldFlag, newFlag) {},
+  onFolderUnicharPropertyChanged(folder, property, oldValue, newValue) {},
+  onFolderPropertyFlagChanged(folder, property, oldFlag, newFlag) {},
   onFolderEvent(folder, event) {
     if (event == "RenameCompleted") {
       // If a folder is renamed, we get an `onFolderAdded` notification for
diff --git a/mail/base/test/browser/browser_folderTreeQuirks.js b/mail/base/test/browser/browser_folderTreeQuirks.js
index aea1533c00..75a2534817 100644
--- a/mail/base/test/browser/browser_folderTreeQuirks.js
+++ b/mail/base/test/browser/browser_folderTreeQuirks.js
@@ -695,6 +695,58 @@ add_task(async function testSearchFolderAddedOnlyOnce() {
   ]);
 });
 
+/**
+ * Tests deferred POP3 accounts are not displayed in All Folders mode, and
+ * that a change in their deferred status updates the folder tree.
+ */
+add_task(async function testDeferredAccount() {
+  let pop3Account = MailServices.accounts.createAccount();
+  let pop3Server = MailServices.accounts.createIncomingServer(
+    `${pop3Account.key}user`,
+    "localhost",
+    "pop3"
+  );
+  pop3Server.QueryInterface(Ci.nsIPop3IncomingServer);
+  pop3Account.incomingServer = pop3Server.QueryInterface(
+    Ci.nsIPop3IncomingServer
+  );
+
+  let pop3RootFolder = pop3Server.rootFolder;
+  let pop3Folders = [
+    pop3RootFolder,
+    pop3RootFolder.getChildNamed("Inbox"),
+    pop3RootFolder.getChildNamed("Trash"),
+  ];
+  let localFolders = [
+    rootFolder,
+    inboxFolder,
+    trashFolder,
+    outboxFolder,
+    folderA,
+    folderB,
+    folderC,
+  ];
+
+  folderPane.activeModes = ["all"];
+  await checkModeListItems("all", [...pop3Folders, ...localFolders]);
+
+  // Defer the account to Local Folders.
+  pop3Server.deferredToAccount = account.key;
+  await checkModeListItems("all", localFolders);
+
+  // Remove and add the All mode again to check that an existing deferred
+  // folder is not shown when the mode initialises.
+  folderPane.activeModes = ["recent"];
+  folderPane.activeModes = ["all"];
+  await checkModeListItems("all", localFolders);
+
+  // Stop deferring the account.
+  pop3Server.deferredToAccount = null;
+  await checkModeListItems("all", [...pop3Folders, ...localFolders]);
+
+  MailServices.accounts.removeAccount(pop3Account, false);
+});
+
 /**
  * We deliberately hide the special [Gmail] folder from the folder tree.
  * Check that it doesn't appear when for a new or existing account.