--- a/toolkit/components/places/PlacesDBUtils.jsm
+++ b/toolkit/components/places/PlacesDBUtils.jsm
@@ -278,16 +278,32 @@ var PlacesDBUtils = {
       { query:
         `DELETE FROM moz_annos WHERE id IN (
           SELECT id FROM moz_annos a
           WHERE NOT EXISTS
             (SELECT id FROM moz_places WHERE id = a.place_id LIMIT 1)
         )`
       },
 
+      // C.1 Fix built-in folders with incorrect parents.
+      { query:
+        `UPDATE moz_bookmarks SET parent = :rootId
+         WHERE guid IN (
+           :menuGuid, :toolbarGuid, :unfiledGuid, :tagsGuid, :mobileGuid
+         ) AND parent <> :rootId`,
+        params: {
+          rootId: PlacesUtils.placesRootId,
+          menuGuid: PlacesUtils.bookmarks.menuGuid,
+          toolbarGuid: PlacesUtils.bookmarks.toolbarGuid,
+          unfiledGuid: PlacesUtils.bookmarks.unfiledGuid,
+          tagsGuid: PlacesUtils.bookmarks.tagsGuid,
+          mobileGuid: PlacesUtils.bookmarks.mobileGuid,
+        }
+      },
+
       // D.1 remove items without a valid place
       // If fk IS NULL we fix them in D.7
       { query:
         `DELETE FROM moz_bookmarks WHERE guid NOT IN (
           :rootGuid, :menuGuid, :toolbarGuid, :unfiledGuid, :tagsGuid  /* skip roots */
         ) AND id IN (
           SELECT b.id FROM moz_bookmarks b
           WHERE fk NOT NULL AND b.type = :bookmark_type

--- a/toolkit/components/places/tests/head_common.js
+++ b/toolkit/components/places/tests/head_common.js
@@ -236,18 +236,21 @@ function clearDB() {
 
 
 /**
  * Dumps the rows of a table out to the console.
  *
  * @param aName
  *        The name of the table or view to output.
  */
-function dump_table(aName) {
-  let stmt = DBConn().createStatement("SELECT * FROM " + aName);
+function dump_table(aName, dbConn) {
+  if (!dbConn) {
+    dbConn = DBConn();
+  }
+  let stmt = dbConn.createStatement("SELECT * FROM " + aName);
 
   print("\n*** Printing data from " + aName);
   let count = 0;
   while (stmt.executeStep()) {
     let columns = stmt.numEntries;
 
     if (count == 0) {
       // Print the column names.

--- a/toolkit/components/places/tests/unit/test_preventive_maintenance.js
+++ b/toolkit/components/places/tests/unit/test_preventive_maintenance.js
@@ -370,16 +370,47 @@ tests.push({
     Assert.equal(bs.getFolderIdForItem(bs.placesRoot), 0);
     Assert.equal(bs.getFolderIdForItem(bs.bookmarksMenuFolder), bs.placesRoot);
     Assert.equal(bs.getFolderIdForItem(bs.tagsFolder), bs.placesRoot);
     Assert.equal(bs.getFolderIdForItem(bs.unfiledBookmarksFolder), bs.placesRoot);
     Assert.equal(bs.getFolderIdForItem(bs.toolbarFolder), bs.placesRoot);
   }
 });
 
+tests.push({
+  name: "C.1",
+  desc: "fix invalid parents for Places folders",
+
+  setup() {
+    // Reparent the roots to something invalid.
+    mDBConn.executeSimpleSQL(`
+      UPDATE moz_bookmarks SET parent = 2
+      WHERE parent = (SELECT id from moz_bookmarks WHERE guid = "${PlacesUtils.bookmarks.rootGuid}")
+    `);
+  },
+
+  async check() {
+    let db = await PlacesUtils.promiseDBConnection();
+
+    let rows = await db.executeCached(`
+      SELECT guid FROM moz_bookmarks
+      WHERE parent = (SELECT id from moz_bookmarks WHERE guid = "${PlacesUtils.bookmarks.rootGuid}")
+    `);
+
+    let guids = rows.map(row => row.getResultByName("guid"));
+    Assert.deepEqual(guids, [
+      PlacesUtils.bookmarks.menuGuid,
+      PlacesUtils.bookmarks.toolbarGuid,
+      PlacesUtils.bookmarks.tagsGuid,
+      PlacesUtils.bookmarks.unfiledGuid,
+      PlacesUtils.bookmarks.mobileGuid,
+    ]);
+  }
+});
+
 // ------------------------------------------------------------------------------
 
 tests.push({
   name: "D.1",
   desc: "Remove items without a valid place",
 
   _validItemId: null,
   _invalidItemId: null,