diff --git a/mail/base/content/folderPane.js b/mail/base/content/folderPane.js
index b357eebb1f..105d376617 100644
--- a/mail/base/content/folderPane.js
+++ b/mail/base/content/folderPane.js
@@ -3406,22 +3406,16 @@ var gFolderTreeController = {
       }
     }
 
-    // xxx useless param
-    function rebuildSummary(aFolder) {
-      // folder is already introduced in our containing function and is
-      // lexically captured and available to us.
+    async function rebuildSummary() {
       if (folder.locked) {
         folder.throwAlertMsg("operationFailedFolderBusy", msgWindow);
         return;
       }
       if (folder.supportsOffline) {
         // Remove the offline store, if any.
-        let offlineStore = folder.filePath;
-        // XXX todo: figure out how to delete a maildir directory async. This
-        // delete causes main thread lockup for large maildir folders.
-        if (offlineStore.exists()) {
-          offlineStore.remove(true);
-        }
+        await IOUtils.remove(folder.filePath.path, { recursive: true }).catch(
+          Cu.reportError
+        );
       }
 
       // We may be rebuilding a folder that is not the displayed one.
diff --git a/mailnews/base/content/folderProps.js b/mailnews/base/content/folderProps.js
index d54f43df4e..2505d34ef3 100644
--- a/mailnews/base/content/folderProps.js
+++ b/mailnews/base/content/folderProps.js
@@ -18,8 +18,12 @@ window.addEventListener("DOMContentLoaded", folderPropsOnLoad);
 document.addEventListener("dialogaccept", folderPropsOKButton);
 document.addEventListener("dialogcancel", folderCancelButton);
 
-// The folderPropsSink is the class that gets notified of an imap folder's properties
-
+/**
+ * The folderPropsSink is the class that gets notified of an imap folder's
+ * properties.
+ *
+ * @implements {nsIMsgImapFolderProps}
+ */
 var gFolderPropsSink = {
   setFolderType(folderTypeString) {
     var typeLabel = document.getElementById("folderType.text");
@@ -243,8 +247,6 @@ function folderPropsOnLoad() {
       gMsgFolder,
       "folderIconColor"
     );
-  } else {
-    dump("passed null for folder, do nothing\n");
   }
 
   if (window.arguments[0].name) {
@@ -253,9 +255,6 @@ function folderPropsOnLoad() {
     // when the dialog is accepted.
     var nameTextbox = document.getElementById("name");
     nameTextbox.value = window.arguments[0].name;
-
-    // name.setSelectionRange(0,-1);
-    // name.focusTextField();
   }
 
   const serverType = window.arguments[0].serverType;
@@ -346,10 +345,8 @@ function folderPropsOnLoad() {
   }
 
   if (serverType == "imap") {
-    var imapFolder = gMsgFolder.QueryInterface(Ci.nsIMsgImapMailFolder);
-    if (imapFolder) {
-      imapFolder.fillInFolderProps(gFolderPropsSink);
-    }
+    let imapFolder = gMsgFolder.QueryInterface(Ci.nsIMsgImapMailFolder);
+    imapFolder.fillInFolderProps(gFolderPropsSink);
 
     let users = [...imapFolder.getOtherUsersWithAccess()];
     if (users.length) {
@@ -358,6 +355,11 @@ function folderPropsOnLoad() {
         ", "
       );
     }
+
+    // Disable "Repair Folder" when offline as that would cause the offline store
+    // to get deleted and redownloaded.
+    document.getElementById("folderRebuildSummaryButton").disabled =
+      gMsgFolder.supportsOffline && Services.io.offline;
   }
 
   var retentionSettings = gMsgFolder.retentionSettings;
@@ -475,5 +477,5 @@ function onUseDefaultRetentionSettings() {
 }
 
 function RebuildSummaryInformation() {
-  window.arguments[0].rebuildSummaryCallback(gMsgFolder);
+  window.arguments[0].rebuildSummaryCallback();
 }