diff --git a/browser/components/places/tests/unit/head_bookmarks.js b/browser/components/places/tests/unit/head_bookmarks.js
index 7113c1eaa26..8eafc649848 100644
--- a/browser/components/places/tests/unit/head_bookmarks.js
+++ b/browser/components/places/tests/unit/head_bookmarks.js
@@ -329,3 +329,15 @@ function flush_main_thread_events()
   while (tm.mainThread.hasPendingEvents())
     tm.mainThread.processNextEvent(false);
 }
+
+// These tests are known to randomly fail due to bug 507790 when database
+// flushes are active, so we turn off syncing for them.
+let randomFailingSyncTests = [
+  "test_browserGlue_smartBookmarks.js",
+];
+let currentTestFilename = do_get_file(_TEST_FILE[0], true).leafName;
+if (randomFailingSyncTests.indexOf(currentTestFilename) != -1) {
+  print("Test " + currentTestFilename + " is known random due to bug 507790, disabling PlacesDBFlush component.");
+  let sync = Cc["@mozilla.org/places/sync;1"].getService(Ci.nsIObserver);
+  sync.observe(null, "places-debug-stop-sync", null);
+}
diff --git a/toolkit/components/places/src/nsPlacesDBFlush.js b/toolkit/components/places/src/nsPlacesDBFlush.js
index ee1afd99208..fdb74c16a27 100644
--- a/toolkit/components/places/src/nsPlacesDBFlush.js
+++ b/toolkit/components/places/src/nsPlacesDBFlush.js
@@ -50,6 +50,8 @@ const Cu = Components.utils;
 
 const kQuitApplication = "quit-application";
 const kSyncFinished = "places-sync-finished";
+const kDebugStopSync = "places-debug-stop-sync";
+const kDebugStartSync = "places-debug-start-sync";
 
 const kSyncPrefName = "places.syncDBTableIntervalInSecs";
 const kDefaultSyncInterval = 120;
@@ -108,6 +110,8 @@ function nsPlacesDBFlush()
   this._os = Cc["@mozilla.org/observer-service;1"].
              getService(Ci.nsIObserverService);
   this._os.addObserver(this, kQuitApplication, false);
+  this._os.addObserver(this, kDebugStopSync, false);
+  this._os.addObserver(this, kDebugStartSync, false);
 
   let (pb2 = this._prefs.QueryInterface(Ci.nsIPrefBranch2)) {
     pb2.addObserver(kSyncPrefName, this, false);
@@ -147,6 +151,9 @@ nsPlacesDBFlush.prototype = {
   {
     if (aTopic == kQuitApplication) {
       this._os.removeObserver(this, kQuitApplication);
+      this._os.removeObserver(this, kDebugStopSync);
+      this._os.removeObserver(this, kDebugStartSync);
+
       let (pb2 = this._prefs.QueryInterface(Ci.nsIPrefBranch2)) {
         pb2.removeObserver(kSyncPrefName, this);
         pb2.removeObserver(kExpireDaysPrefName, this);
@@ -195,6 +202,13 @@ nsPlacesDBFlush.prototype = {
       if (this._expireDays <= 0)
         this._expireDays = kDefaultExpireDays;
     }
+    else if (aTopic == kDebugStopSync) {
+      this._syncStopped = true;
+    }
+    else if (aTopic == kDebugStartSync) {
+      if (_syncStopped in this)
+        delete this._syncStopped;
+    }
   },
 
   //////////////////////////////////////////////////////////////////////////////
@@ -338,7 +352,7 @@ nsPlacesDBFlush.prototype = {
   _flushWithQueries: function DBFlush_flushWithQueries(aQueryNames)
   {
     // No need to do extra work if we are in batch mode
-    if (this._inBatchMode)
+    if (this._inBatchMode || this._syncStopped)
       return;
 
     let statements = [];
diff --git a/toolkit/components/places/tests/bookmarks/head_bookmarks.js b/toolkit/components/places/tests/bookmarks/head_bookmarks.js
index 5c7bc422cb9..f530e16d65f 100644
--- a/toolkit/components/places/tests/bookmarks/head_bookmarks.js
+++ b/toolkit/components/places/tests/bookmarks/head_bookmarks.js
@@ -164,3 +164,19 @@ function flush_main_thread_events()
   while (tm.mainThread.hasPendingEvents())
     tm.mainThread.processNextEvent(false);
 }
+
+// These tests are known to randomly fail due to bug 507790 when database
+// flushes are active, so we turn off syncing for them.
+let randomFailingSyncTests = [
+  "test_384228.js",
+  "test_395593.js",
+  "test_405938_restore_queries.js",
+  "test_423515_forceCopyShortcuts.js",
+  "test_448584.js",
+];
+let currentTestFilename = do_get_file(_TEST_FILE[0], true).leafName;
+if (randomFailingSyncTests.indexOf(currentTestFilename) != -1) {
+  print("Test " + currentTestFilename + " is known random due to bug 507790, disabling PlacesDBFlush component.");
+  let sync = Cc["@mozilla.org/places/sync;1"].getService(Ci.nsIObserver);
+  sync.observe(null, "places-debug-stop-sync", null);
+}
diff --git a/toolkit/components/places/tests/queries/head_queries.js b/toolkit/components/places/tests/queries/head_queries.js
index e0e5845a93d..f74420617a7 100644
--- a/toolkit/components/places/tests/queries/head_queries.js
+++ b/toolkit/components/places/tests/queries/head_queries.js
@@ -562,3 +562,15 @@ function flush_main_thread_events()
   while (tm.mainThread.hasPendingEvents())
     tm.mainThread.processNextEvent(false);
 }
+
+// These tests are known to randomly fail due to bug 507790 when database
+// flushes are active, so we turn off syncing for them.
+let randomFailingSyncTests = [
+  " test_results-as-visits.js",
+];
+let currentTestFilename = do_get_file(_TEST_FILE[0], true).leafName;
+if (randomFailingSyncTests.indexOf(currentTestFilename) != -1) {
+  print("Test " + currentTestFilename + " is known random due to bug 507790, disabling PlacesDBFlush component.");
+  let sync = Cc["@mozilla.org/places/sync;1"].getService(Ci.nsIObserver);
+  sync.observe(null, "places-debug-stop-sync", null);
+}
diff --git a/toolkit/components/places/tests/queries/test_results-as-visit.js b/toolkit/components/places/tests/queries/test_results-as-visit.js
index 11aac6e055f..f9bd435f6b4 100644
--- a/toolkit/components/places/tests/queries/test_results-as-visit.js
+++ b/toolkit/components/places/tests/queries/test_results-as-visit.js
@@ -64,9 +64,6 @@ function createTestData() {
   * This test will test Queries that use relative search terms and URI options
   */
  function run_test() {
-   /* Temporarly disabled till we figure out what's up. See  Bug 511860 */
-   return;
-
    createTestData();
    populateDB(testData);
    var query = histsvc.getNewQuery();
diff --git a/toolkit/components/places/tests/unit/head_bookmarks.js b/toolkit/components/places/tests/unit/head_bookmarks.js
index 80be47862e8..3c1f47677b8 100644
--- a/toolkit/components/places/tests/unit/head_bookmarks.js
+++ b/toolkit/components/places/tests/unit/head_bookmarks.js
@@ -206,3 +206,19 @@ function flush_main_thread_events()
   while (tm.mainThread.hasPendingEvents())
     tm.mainThread.processNextEvent(false);
 }
+
+// These tests are known to randomly fail due to bug 507790 when database
+// flushes are active, so we turn off syncing for them.
+let randomFailingSyncTests = [
+  "test_annotations.js",
+  "test_multi_word_tags.js",
+  "test_removeVisitsByTimeframe.js",
+  "test_tagging.js",
+  "test_utils_getURLsForContainerNode.js",
+];
+let currentTestFilename = do_get_file(_TEST_FILE[0], true).leafName;
+if (randomFailingSyncTests.indexOf(currentTestFilename) != -1) {
+  print("Test " + currentTestFilename + " is known random due to bug 507790, disabling PlacesDBFlush component.");
+  let sync = Cc["@mozilla.org/places/sync;1"].getService(Ci.nsIObserver);
+  sync.observe(null, "places-debug-stop-sync", null);
+}