--- a/toolkit/components/places/tests/sync/head_sync.js
+++ b/toolkit/components/places/tests/sync/head_sync.js
@@ -1,28 +1,29 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 ChromeUtils.import("resource://gre/modules/Services.jsm");
-ChromeUtils.import("resource://gre/modules/CanonicalJSON.jsm");
 
 // Import common head.
 {
   /* import-globals-from ../head_common.js */
   let commonFile = do_get_file("../head_common.js", false);
   let uri = Services.io.newFileURI(commonFile);
   Services.scriptloader.loadSubScript(uri.spec, this);
 }
 
 // Put any other stuff relative to this test folder below.
 
+ChromeUtils.import("resource://gre/modules/CanonicalJSON.jsm");
 ChromeUtils.import("resource://gre/modules/Log.jsm");
 ChromeUtils.import("resource://gre/modules/ObjectUtils.jsm");
 ChromeUtils.import("resource://gre/modules/PlacesSyncUtils.jsm");
 ChromeUtils.import("resource://gre/modules/SyncedBookmarksMirror.jsm");
+ChromeUtils.import("resource://testing-common/FileTestUtils.jsm");
 ChromeUtils.import("resource://testing-common/httpd.js");
 
 // These titles are defined in Database::CreateBookmarkRoots
 const BookmarksMenuTitle = "menu";
 const BookmarksToolbarTitle = "toolbar";
 const UnfiledBookmarksTitle = "unfiled";
 const MobileBookmarksTitle = "mobile";
 
@@ -239,8 +240,17 @@ BookmarkObserver.prototype = {
   },
 };
 
 function expectBookmarkChangeNotifications(options) {
   let observer = new BookmarkObserver(options);
   PlacesUtils.bookmarks.addObserver(observer);
   return observer;
 }
+
+// Copies a support file to a temporary fixture file, allowing the support
+// file to be reused for multiple tests.
+async function setupFixtureFile(fixturePath) {
+  let fixtureFile = do_get_file(fixturePath);
+  let tempFile = FileTestUtils.getTempFile(fixturePath);
+  await OS.File.copy(fixtureFile.path, tempFile.path);
+  return tempFile;
+}

--- a/toolkit/components/places/tests/sync/test_bookmark_mirror_migration.js
+++ b/toolkit/components/places/tests/sync/test_bookmark_mirror_migration.js
@@ -1,14 +1,14 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 // Migrations between 1 and 2 discard the entire database.
 add_task(async function test_migrate_from_1_to_2() {
-  let dbFile = do_get_file("mirror_v1.sqlite");
+  let dbFile = await setupFixtureFile("mirror_v1.sqlite");
   let telemetryEvents = [];
   let buf = await SyncedBookmarksMirror.open({
     path: dbFile.path,
     recordTelemetryEvent(object, method, value, extra) {
       telemetryEvents.push({ object, method, value, extra });
     },
   });
   deepEqual(telemetryEvents, [{
@@ -16,17 +16,17 @@ add_task(async function test_migrate_fro
     method: "open",
     value: "retry",
     extra: { why: "corrupt" },
   }]);
   await buf.finalize();
 });
 
 add_task(async function test_database_corrupt() {
-  let corruptFile = do_get_file("mirror_corrupt.sqlite");
+  let corruptFile = await setupFixtureFile("mirror_corrupt.sqlite");
   let telemetryEvents = [];
   let buf = await SyncedBookmarksMirror.open({
     path: corruptFile.path,
     recordTelemetryEvent(object, method, value, extra) {
       telemetryEvents.push({ object, method, value, extra });
     },
   });
   deepEqual(telemetryEvents, [{
@@ -34,17 +34,17 @@ add_task(async function test_database_co
     method: "open",
     value: "retry",
     extra: { why: "corrupt" },
   }]);
   await buf.finalize();
 });
 
 add_task(async function test_database_readonly() {
-  let dbFile = do_get_file("mirror_v1.sqlite");
+  let dbFile = await setupFixtureFile("mirror_v1.sqlite");
   try {
     await OS.File.setPermissions(dbFile.path, {
       unixMode: 0o400,
       winAttributes: { readOnly: true },
     });
   } catch (ex) {
     if (ex instanceof OS.File.Error &&
         ex.unixErrno == OS.Constants.libc.EPERM) {