diff --git a/services/.eslintrc.js b/services/.eslintrc.js
index a42f4047f8c2..c11de0d4b01e 100644
--- a/services/.eslintrc.js
+++ b/services/.eslintrc.js
@@ -21,7 +21,6 @@ module.exports = {
     "no-redeclare": "warn",
     "no-unreachable": "warn",
     "no-unsafe-finally": "warn",
-    "no-unused-vars": "warn",
     "no-useless-call": "warn"
   }
 };
diff --git a/services/cloudsync/CloudSyncBookmarks.jsm b/services/cloudsync/CloudSyncBookmarks.jsm
index fb4438f4d5ee..4cb0bc7a7f60 100644
--- a/services/cloudsync/CloudSyncBookmarks.jsm
+++ b/services/cloudsync/CloudSyncBookmarks.jsm
@@ -144,7 +144,6 @@ var Bookmarks = function() {
 
   let getRootFolder = function(name) {
     let ROOT_FOLDER_ANNO = "cloudsync/rootFolder/" + name;
-    let ROOT_SHORTCUT_ANNO = "cloudsync/rootShortcut/" + name;
     let deferred = Promise.defer();
 
     function checkRootFolder(folderIds) {
@@ -171,7 +170,6 @@ var Bookmarks = function() {
     let ROOT_SHORTCUT_ANNO = "cloudsync/rootShortcut/" + name;
 
     let deferred = Promise.defer();
-    let placesRootId = PlacesUtils.placesRootId;
 
     function getRootShortcutId() {
       return PlacesWrapper.getLocalIdsWithAnnotation(ROOT_SHORTCUT_ANNO);
diff --git a/services/cloudsync/CloudSyncTabs.jsm b/services/cloudsync/CloudSyncTabs.jsm
index 0b35c21932bb..74e98187a175 100644
--- a/services/cloudsync/CloudSyncTabs.jsm
+++ b/services/cloudsync/CloudSyncTabs.jsm
@@ -220,19 +220,6 @@ this.Tabs = function() {
 
   let tabCache = new TabCache();
 
-  let getWindowEnumerator = function() {
-    return Services.wm.getEnumerator("navigator:browser");
-  };
-
-  let shouldSkipWindow = function(win) {
-    return win.closed ||
-           PrivateBrowsingUtils.isWindowPrivate(win);
-  };
-
-  let getTabState = function(tab) {
-    return JSON.parse(Session.getTabState(tab));
-  };
-
   let getLocalTabs = function(filter) {
     let deferred = Promise.defer();
 
diff --git a/services/common/modules-testing/storageserver.js b/services/common/modules-testing/storageserver.js
index cf5a8618788a..a3c0f0541b16 100644
--- a/services/common/modules-testing/storageserver.js
+++ b/services/common/modules-testing/storageserver.js
@@ -345,7 +345,7 @@ StorageServerCollection.prototype = {
    */
   bsos: function bsos(filter) {
     let os = [];
-    for (let [id, bso] of Object.entries(this._bsos)) {
+    for (let bso of Object.values(this._bsos)) {
       if (!bso.deleted) {
         os.push(bso);
       }
@@ -440,7 +440,7 @@ StorageServerCollection.prototype = {
   count: function count(options) {
     options = options || {};
     let c = 0;
-    for (let [id, bso] of Object.entries(this._bsos)) {
+    for (let bso of Object.values(this._bsos)) {
       if (bso.modified && this._inResultSet(bso, options)) {
         c++;
       }
@@ -598,7 +598,7 @@ StorageServerCollection.prototype = {
     }
 
     let deleted = [];
-    for (let [id, bso] of Object.entries(this._bsos)) {
+    for (let bso of Object.values(this._bsos)) {
       if (this._inResultSet(bso, options)) {
         this._log.debug("Deleting " + JSON.stringify(bso));
         deleted.push(bso.id);
@@ -730,8 +730,6 @@ StorageServerCollection.prototype = {
   },
 
   postHandler: function postHandler(request, response) {
-    let options = this.parseOptions(request);
-
     if (!request.hasHeader("content-type")) {
       this._log.info("No Content-Type request header!");
       throw HTTP_400;
@@ -1319,7 +1317,7 @@ StorageServer.prototype = {
       throw HTTP_404;
     }
 
-    let [all, version, userPath, first, rest] = parts;
+    let [, version, userPath, first, rest] = parts;
     if (version != STORAGE_API_VERSION) {
       this._log.debug("StorageServer: Unknown version.");
       throw HTTP_404;
@@ -1427,7 +1425,7 @@ StorageServer.prototype = {
         this._log.warn("StorageServer: Unknown storage operation " + rest);
         throw HTTP_404;
       }
-      let [all, collection, bsoID] = match;
+      let [, collection, bsoID] = match;
       let coll = this.getCollection(username, collection);
       let collectionExisted = !!coll;
 
diff --git a/services/common/tests/unit/test_async_querySpinningly.js b/services/common/tests/unit/test_async_querySpinningly.js
index 76d4ffbbb135..50808e86ce3f 100644
--- a/services/common/tests/unit/test_async_querySpinningly.js
+++ b/services/common/tests/unit/test_async_querySpinningly.js
@@ -85,9 +85,9 @@ function run_test() {
   _("Generate an execution error");
   let query = "INSERT INTO moz_formhistory (fieldname, value) VALUES ('one', NULL)";
   let stmt = Svc.Form.DBConnection.createStatement(query);
-  let r11, except;
+  let except;
   try {
-    r11 = Async.querySpinningly(stmt);
+    Async.querySpinningly(stmt);
   } catch (e) {
     except = e;
   }
diff --git a/services/common/tests/unit/test_blocklist_certificates.js b/services/common/tests/unit/test_blocklist_certificates.js
index 5da16f613e56..cf5ee9d03889 100644
--- a/services/common/tests/unit/test_blocklist_certificates.js
+++ b/services/common/tests/unit/test_blocklist_certificates.js
@@ -64,7 +64,7 @@ add_task(function* test_something() {
   server.registerPathHandler(recordsPath, handleResponse);
 
   // Test an empty db populates
-  let result = yield OneCRLBlocklistClient.maybeSync(2000, Date.now());
+  yield OneCRLBlocklistClient.maybeSync(2000, Date.now());
 
   // Open the collection, verify it's been populated:
   // Our test data has a single record; it should be in the local collection
diff --git a/services/common/tests/unit/test_blocklist_clients.js b/services/common/tests/unit/test_blocklist_clients.js
index ca5aa5eaeecb..997b590f7863 100644
--- a/services/common/tests/unit/test_blocklist_clients.js
+++ b/services/common/tests/unit/test_blocklist_clients.js
@@ -121,7 +121,7 @@ function run_test() {
 add_task(function* test_records_obtained_from_server_are_stored_in_db() {
   for (let {client} of gBlocklistClients) {
     // Test an empty db populates
-    let result = yield client.maybeSync(2000, Date.now());
+    yield client.maybeSync(2000, Date.now());
 
     // Open the collection, verify it's been populated:
     // Our test data has a single record; it should be in the local collection
@@ -139,7 +139,7 @@ add_task(function* test_list_is_written_to_file_in_profile() {
     const profFile = FileUtils.getFile(KEY_PROFILEDIR, [filename]);
     strictEqual(profFile.exists(), false);
 
-    let result = yield client.maybeSync(2000, Date.now());
+    yield client.maybeSync(2000, Date.now());
 
     strictEqual(profFile.exists(), true);
     const content = yield readJSON(profFile.path);
@@ -150,7 +150,6 @@ add_task(clear_state);
 
 add_task(function* test_current_server_time_is_saved_in_pref() {
   for (let {client} of gBlocklistClients) {
-    const before = Services.prefs.getIntPref(client.lastCheckTimePref);
     const serverTime = Date.now();
     yield client.maybeSync(2000, serverTime);
     const after = Services.prefs.getIntPref(client.lastCheckTimePref);
@@ -162,7 +161,6 @@ add_task(clear_state);
 add_task(function* test_update_json_file_when_addons_has_changes() {
   for (let {client, filename, testData} of gBlocklistClients) {
     yield client.maybeSync(2000, Date.now() - 1000);
-    const before = Services.prefs.getIntPref(client.lastCheckTimePref);
     const profFile = FileUtils.getFile(KEY_PROFILEDIR, [filename]);
     const fileLastModified = profFile.lastModifiedTime = profFile.lastModifiedTime - 1000;
     const serverTime = Date.now();
@@ -198,7 +196,6 @@ add_task(clear_state);
 add_task(function* test_do_nothing_when_blocklist_is_up_to_date() {
   for (let {client, filename} of gBlocklistClients) {
     yield client.maybeSync(2000, Date.now() - 1000);
-    const before = Services.prefs.getIntPref(client.lastCheckTimePref);
     const profFile = FileUtils.getFile(KEY_PROFILEDIR, [filename]);
     const fileLastModified = profFile.lastModifiedTime = profFile.lastModifiedTime - 1000;
     const serverTime = Date.now();
diff --git a/services/common/tests/unit/test_blocklist_pinning.js b/services/common/tests/unit/test_blocklist_pinning.js
index 54229f5e4870..a270eddc82a1 100644
--- a/services/common/tests/unit/test_blocklist_pinning.js
+++ b/services/common/tests/unit/test_blocklist_pinning.js
@@ -98,7 +98,7 @@ add_task(function* test_something() {
   ok(!sss.isSecureHost(sss.HEADER_HSTS, "five.example.com", 0));
 
   // Test an empty db populates
-  let result = yield PinningPreloadClient.maybeSync(2000, Date.now());
+  yield PinningPreloadClient.maybeSync(2000, Date.now());
 
   let connection = yield FirefoxAdapter.openConnection({path: KINTO_STORAGE_PATH});
 
diff --git a/services/common/tests/unit/test_blocklist_signatures.js b/services/common/tests/unit/test_blocklist_signatures.js
index 5a08761aeebf..ca1f46306a11 100644
--- a/services/common/tests/unit/test_blocklist_signatures.js
+++ b/services/common/tests/unit/test_blocklist_signatures.js
@@ -143,7 +143,6 @@ add_task(function* test_check_signatures() {
 
     for (let key of Object.keys(responses)) {
       const keyParts = key.split(":");
-      const method = keyParts[0];
       const valueParts = keyParts[1].split("?");
       const path = valueParts[0];
 
diff --git a/services/common/tests/unit/test_hawkclient.js b/services/common/tests/unit/test_hawkclient.js
index 9d24db0205e1..1a91cc6a2484 100644
--- a/services/common/tests/unit/test_hawkclient.js
+++ b/services/common/tests/unit/test_hawkclient.js
@@ -202,7 +202,7 @@ add_task(function* test_offset_after_request() {
 
   do_check_eq(client.localtimeOffsetMsec, 0);
 
-  let response = yield client.request("/foo", method, TEST_CREDS);
+  yield client.request("/foo", method, TEST_CREDS);
   // Should be about an hour off
   do_check_true(Math.abs(client.localtimeOffsetMsec + HOUR_MS) < SECOND_MS);
 
@@ -236,9 +236,6 @@ add_task(function* test_offset_in_hawk_header() {
   });
 
   let client = new HawkClient(server.baseURI);
-  function getOffset() {
-    return client.localtimeOffsetMsec;
-  }
 
   client.now = () => {
     return Date.now() + 12 * HOUR_MS;
@@ -316,9 +313,6 @@ add_task(function* test_retry_request_on_fail() {
   });
 
   let client = new HawkClient(server.baseURI);
-  function getOffset() {
-    return client.localtimeOffsetMsec;
-  }
 
   client.now = () => {
     return Date.now() + 12 * HOUR_MS;
@@ -360,9 +354,6 @@ add_task(function* test_multiple_401_retry_once() {
   });
 
   let client = new HawkClient(server.baseURI);
-  function getOffset() {
-    return client.localtimeOffsetMsec;
-  }
 
   client.now = () => {
     return Date.now() - 12 * HOUR_MS;
@@ -402,9 +393,6 @@ add_task(function* test_500_no_retry() {
   });
 
   let client = new HawkClient(server.baseURI);
-  function getOffset() {
-    return client.localtimeOffsetMsec;
-  }
 
   // Throw off the clock so the HawkClient would want to retry the request if
   // it could
@@ -464,9 +452,6 @@ add_task(function* test_401_then_500() {
   });
 
   let client = new HawkClient(server.baseURI);
-  function getOffset() {
-    return client.localtimeOffsetMsec;
-  }
 
   client.now = () => {
     return Date.now() - 12 * HOUR_MS;
diff --git a/services/common/tests/unit/test_hawkrequest.js b/services/common/tests/unit/test_hawkrequest.js
index 1f0e9ec8d0f3..a88bc946b83d 100644
--- a/services/common/tests/unit/test_hawkrequest.js
+++ b/services/common/tests/unit/test_hawkrequest.js
@@ -57,7 +57,6 @@ add_test(function test_intl_accept_language() {
   setLanguagePref(languages[testCount]);
 
   function checkLanguagePref() {
-    var _done = false;
     CommonUtils.nextTick(function() {
       // Ensure we're only called for the number of entries in languages[].
       do_check_true(testCount < languages.length);
@@ -186,7 +185,6 @@ add_test(function test_hawk_language_pref_changed() {
   });
 
   let url = server.baseURI + "/foo";
-  let postData = {};
   let request;
 
   setLanguage(languages[0]);
diff --git a/services/common/tests/unit/test_logmanager.js b/services/common/tests/unit/test_logmanager.js
index 13e5caa0a655..27d4a76668d5 100644
--- a/services/common/tests/unit/test_logmanager.js
+++ b/services/common/tests/unit/test_logmanager.js
@@ -83,7 +83,7 @@ add_task(function* test_SharedLogs() {
   let lm2 = new LogManager("log-manager-2.test.", ["TestLog3"], "test");
 
   let log = Log.repository.getLogger("TestLog3");
-  let [capp, dapp, fapps] = getAppenders(log);
+  let [capp, dapp, ] = getAppenders(log);
 
   // console and dump appenders should be "trace" as it is more verbose than
   // "debug"
diff --git a/services/common/tests/unit/test_storage_adapter.js b/services/common/tests/unit/test_storage_adapter.js
index 5c23d257475c..066b05f68398 100644
--- a/services/common/tests/unit/test_storage_adapter.js
+++ b/services/common/tests/unit/test_storage_adapter.js
@@ -248,7 +248,6 @@ add_test(function test_creation_from_empty_db() {
   add_test(function test_create_from_empty_db() {
     // place an empty kinto db file in the profile
     let profile = do_get_profile();
-    let kintoDB = do_get_kinto_db();
 
     let emptyDB = do_get_file("test_storage_adapter/empty.sqlite");
     emptyDB.copyTo(profile, kintoFilename);
diff --git a/services/common/tests/unit/test_storage_server.js b/services/common/tests/unit/test_storage_server.js
index 8609a0fa50c5..ae1099911eac 100644
--- a/services/common/tests/unit/test_storage_server.js
+++ b/services/common/tests/unit/test_storage_server.js
@@ -173,8 +173,8 @@ add_test(function test_url_parsing() {
   do_check_eq(rest, undefined);
 
   parts = server.storageRE.exec("storage");
-  let storage, collection, id;
-  [all, storage, collection, id] = parts;
+  let collection;
+  [all, , collection, ] = parts;
   do_check_eq(all, "storage");
   do_check_eq(collection, undefined);
 
@@ -414,7 +414,7 @@ add_test(function test_bso_delete_exists() {
   server.startSynchronous();
 
   let coll = server.user("123").createCollection("test");
-  let bso = coll.insert("myid", {foo: "bar"});
+  coll.insert("myid", {foo: "bar"});
   let timestamp = coll.timestamp;
 
   server.callback.onItemDeleted = function onDeleted(username, collection, id) {
diff --git a/services/common/utils.js b/services/common/utils.js
index d1ab244d331a..953b79b33bd5 100644
--- a/services/common/utils.js
+++ b/services/common/utils.js
@@ -237,7 +237,6 @@ this.CommonUtils = {
    */
   encodeBase32: function encodeBase32(bytes) {
     const key = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
-    let quanta = Math.floor(bytes.length / 5);
     let leftover = bytes.length % 5;
 
     // Pad the last quantum with zeros so the length is a multiple of 5.
diff --git a/services/crypto/modules/utils.js b/services/crypto/modules/utils.js
index dca1d3b8381c..edf0794dedf0 100644
--- a/services/crypto/modules/utils.js
+++ b/services/crypto/modules/utils.js
@@ -134,7 +134,6 @@ this.CryptoUtils = {
    * HMAC-based Key Derivation (RFC 5869).
    */
   hkdf: function hkdf(ikm, xts, info, len) {
-    const BLOCKSIZE = 256 / 8;
     if (typeof xts === undefined)
       xts = String.fromCharCode(0, 0, 0, 0, 0, 0, 0, 0,
                                 0, 0, 0, 0, 0, 0, 0, 0,
diff --git a/services/fxaccounts/FxAccounts.jsm b/services/fxaccounts/FxAccounts.jsm
index 0682d6baa379..cfe84f74bcc9 100644
--- a/services/fxaccounts/FxAccounts.jsm
+++ b/services/fxaccounts/FxAccounts.jsm
@@ -742,7 +742,7 @@ FxAccountsInternal.prototype = {
   _destroyAllOAuthTokens(tokenInfos) {
     // let's just destroy them all in parallel...
     let promises = [];
-    for (let [key, tokenInfo] of Object.entries(tokenInfos || {})) {
+    for (let tokenInfo of Object.values(tokenInfos || {})) {
       promises.push(this._destroyOAuthToken(tokenInfo));
     }
     return Promise.all(promises);
@@ -953,7 +953,6 @@ FxAccountsInternal.prototype = {
 
   getAssertionFromCert(data, keyPair, cert, audience) {
     log.debug("getAssertionFromCert");
-    let payload = {};
     let d = Promise.defer();
     let options = {
       duration: ASSERTION_LIFETIME,
diff --git a/services/fxaccounts/FxAccountsManager.jsm b/services/fxaccounts/FxAccountsManager.jsm
index f3044833b24f..5b9aaef109fa 100644
--- a/services/fxaccounts/FxAccountsManager.jsm
+++ b/services/fxaccounts/FxAccountsManager.jsm
@@ -458,8 +458,6 @@ this.FxAccountsManager = {
       return this._error(ERROR_OFFLINE);
     }
 
-    let deferred = Promise.defer();
-
     if (!aEmail) {
       return this._error(ERROR_INVALID_EMAIL);
     }
diff --git a/services/fxaccounts/tests/xpcshell/test_accounts.js b/services/fxaccounts/tests/xpcshell/test_accounts.js
index 1a321c558d47..505623fc6264 100644
--- a/services/fxaccounts/tests/xpcshell/test_accounts.js
+++ b/services/fxaccounts/tests/xpcshell/test_accounts.js
@@ -1004,7 +1004,7 @@ add_task(function* test_sign_out_without_device() {
   delete credentials.deviceId;
   yield fxa.internal.setSignedInUser(credentials);
 
-  const user = yield fxa.internal.getUserAccountData();
+  yield fxa.internal.getUserAccountData();
 
   const spy = {
     signOut: { count: 0, args: [] },
diff --git a/services/fxaccounts/tests/xpcshell/test_accounts_device_registration.js b/services/fxaccounts/tests/xpcshell/test_accounts_device_registration.js
index 11c845188892..15c7caf284fe 100644
--- a/services/fxaccounts/tests/xpcshell/test_accounts_device_registration.js
+++ b/services/fxaccounts/tests/xpcshell/test_accounts_device_registration.js
@@ -182,7 +182,6 @@ add_task(function* test_updateDeviceRegistration_with_new_device() {
 
 add_task(function* test_updateDeviceRegistration_with_existing_device() {
   const deviceName = "phil's device";
-  const deviceType = "desktop";
 
   const credentials = getTestUser("pb");
   const fxa = new MockFxAccounts({ name: deviceName });
@@ -363,7 +362,6 @@ add_task(function* test_updateDeviceRegistration_with_device_session_conflict_er
 
 add_task(function* test_updateDeviceRegistration_with_unrecoverable_error() {
   const deviceName = "foo";
-  const deviceType = "bar";
 
   const credentials = getTestUser("baz");
   delete credentials.deviceId;
diff --git a/services/fxaccounts/tests/xpcshell/test_client.js b/services/fxaccounts/tests/xpcshell/test_client.js
index 224276851725..61eba826183c 100644
--- a/services/fxaccounts/tests/xpcshell/test_client.js
+++ b/services/fxaccounts/tests/xpcshell/test_client.js
@@ -586,7 +586,6 @@ add_task(function* test_signCertificate() {
 });
 
 add_task(function* test_accountExists() {
-  let sessionMessage = JSON.stringify({sessionToken: FAKE_SESSION_TOKEN});
   let existsMessage = JSON.stringify({error: "wrong password", code: 400, errno: 103});
   let doesntExistMessage = JSON.stringify({error: "no such account", code: 400, errno: 102});
   let emptyMessage = "{}";
diff --git a/services/fxaccounts/tests/xpcshell/test_credentials.js b/services/fxaccounts/tests/xpcshell/test_credentials.js
index 06314bb57a37..0e9ac57bf19a 100644
--- a/services/fxaccounts/tests/xpcshell/test_credentials.js
+++ b/services/fxaccounts/tests/xpcshell/test_credentials.js
@@ -67,8 +67,6 @@ add_task(function* test_onepw_setup_credentials() {
 });
 
 add_task(function* test_client_stretch_kdf() {
-  let pbkdf2 = CryptoUtils.pbkdf2Generate;
-  let hkdf = CryptoUtils.hkdf;
   let expected = vectors["client stretch-KDF"];
 
   let email = h2s(expected.email);
diff --git a/services/fxaccounts/tests/xpcshell/test_profile.js b/services/fxaccounts/tests/xpcshell/test_profile.js
index 179b13c450a8..ff008cc8f530 100644
--- a/services/fxaccounts/tests/xpcshell/test_profile.js
+++ b/services/fxaccounts/tests/xpcshell/test_profile.js
@@ -184,7 +184,7 @@ add_task(function* fetchAndCacheProfileOnce() {
   let profile = CreateFxAccountsProfile(null, client);
 
   let request1 = profile._fetchAndCacheProfile();
-  let request2 = profile._fetchAndCacheProfile();
+  profile._fetchAndCacheProfile();
 
   // should be one request made to fetch the profile (but the promise returned
   // by it remains unresolved)
diff --git a/services/sync/modules/SyncedTabs.jsm b/services/sync/modules/SyncedTabs.jsm
index 8c8d461a7a3e..a8340dfe7363 100644
--- a/services/sync/modules/SyncedTabs.jsm
+++ b/services/sync/modules/SyncedTabs.jsm
@@ -110,10 +110,9 @@ let SyncedTabsInternal = {
     let engine = Weave.Service.engineManager.get("tabs");
 
     let seenURLs = new Set();
-    let parentIndex = 0;
     let ntabs = 0;
 
-    for (let [guid, client] of Object.entries(engine.getAllClients())) {
+    for (let client of Object.values(engine.getAllClients())) {
       if (!Weave.Service.clientsEngine.remoteClientExists(client.id)) {
         continue;
       }
diff --git a/services/sync/modules/bookmark_validator.js b/services/sync/modules/bookmark_validator.js
index 56f733c35419..7897fa608e17 100644
--- a/services/sync/modules/bookmark_validator.js
+++ b/services/sync/modules/bookmark_validator.js
@@ -324,7 +324,6 @@ class BookmarkValidator {
     let deletedRecords = [];
 
     let folders = [];
-    let problems = [];
 
     let problemData = new BookmarkProblemData();
 
@@ -620,8 +619,6 @@ class BookmarkValidator {
 
     this._validateClient(problemData, clientRecords);
 
-    let matches = [];
-
     let allRecords = new Map();
     let serverDeletedLookup = new Set(inspectionInfo.deletedRecords.map(r => r.id));
 
diff --git a/services/sync/modules/collection_validator.js b/services/sync/modules/collection_validator.js
index d8daa6ed0d29..f9dacca5e604 100644
--- a/services/sync/modules/collection_validator.js
+++ b/services/sync/modules/collection_validator.js
@@ -153,7 +153,6 @@ class CollectionValidator {
       }
     }
 
-    let recordPairs = [];
     let seenClient = new Map();
     for (let record of clientItems) {
       let id = record[this.idProp];
diff --git a/services/sync/modules/engines/bookmarks.js b/services/sync/modules/engines/bookmarks.js
index f9c201a02aaa..e85ac360e513 100644
--- a/services/sync/modules/engines/bookmarks.js
+++ b/services/sync/modules/engines/bookmarks.js
@@ -336,7 +336,7 @@ BookmarksEngine.prototype = {
     }
 
     for (let [node, parent] of walkBookmarksRoots(tree)) {
-      let {guid, id, type: placeType} = node;
+      let {guid, type: placeType} = node;
       guid = PlacesSyncUtils.bookmarks.guidToSyncId(guid);
       let key;
       switch (placeType) {
diff --git a/services/sync/modules/identity.js b/services/sync/modules/identity.js
index e6760ba9b1cd..dab6baf04806 100644
--- a/services/sync/modules/identity.js
+++ b/services/sync/modules/identity.js
@@ -295,7 +295,6 @@ IdentityManager.prototype = {
 
     // Clear any cached Sync Key Bundle and regenerate it.
     this._syncKeyBundle = null;
-    let bundle = this.syncKeyBundle;
 
     this._syncKeyUpdated = true;
   },
diff --git a/services/sync/modules/resource.js b/services/sync/modules/resource.js
index 933669eb802d..19c63c89c407 100644
--- a/services/sync/modules/resource.js
+++ b/services/sync/modules/resource.js
@@ -163,7 +163,7 @@ AsyncResource.prototype = {
       this._log.debug("No authenticator found.");
     }
 
-    for (let [key, value] of Object.entries(headers)) {
+    for (let key of Object.values(headers)) {
       if (key == "authorization")
         this._log.trace("HTTP Header " + key + ": ***** (suppressed)");
       else
diff --git a/services/sync/modules/service.js b/services/sync/modules/service.js
index 82cfef68b77f..0829441c11e3 100644
--- a/services/sync/modules/service.js
+++ b/services/sync/modules/service.js
@@ -616,7 +616,7 @@ Sync11Service.prototype = {
             let cryptoResp = cryptoKeys.fetch(this.resource(this.cryptoKeysURL)).response;
 
             if (cryptoResp.success) {
-              let keysChanged = this.handleFetchedKeys(syncKeyBundle, cryptoKeys);
+              this.handleFetchedKeys(syncKeyBundle, cryptoKeys);
               return true;
             } else if (cryptoResp.status == 404) {
               // On failure, ask to generate new keys and upload them.
@@ -1092,8 +1092,6 @@ Sync11Service.prototype = {
   // Stuff we need to do after login, before we can really do
   // anything (e.g. key setup).
   _remoteSetup: function _remoteSetup(infoResponse) {
-    let reset = false;
-
     if (!this._fetchServerConfiguration()) {
       return false;
     }
@@ -1317,7 +1315,7 @@ Sync11Service.prototype = {
       synchronizer.sync(engineNamesToSync);
       // wait() throws if the first argument is truthy, which is exactly what
       // we want.
-      let result = cb.wait();
+      cb.wait();
 
       histogram = Services.telemetry.getHistogramById("WEAVE_COMPLETE_SUCCESS_COUNT");
       histogram.add(1);
@@ -1505,7 +1503,7 @@ Sync11Service.prototype = {
     this.upgradeSyncKey(this.syncID);
 
     // Wipe the server.
-    let wipeTimestamp = this.wipeServer();
+    this.wipeServer();
 
     // Upload a new meta/global record.
     let meta = new WBORecord("meta", "global");
@@ -1521,8 +1519,6 @@ Sync11Service.prototype = {
     this.uploadMetaGlobal(meta);
 
     // Wipe everything we know about except meta because we just uploaded it
-    let engines = [this.clientsEngine].concat(this.engineManager.getAll());
-    let collections = engines.map(engine => engine.name);
     // TODO: there's a bug here. We should be calling resetClient, no?
 
     // Generate, upload, and download new keys. Do this last so we don't wipe
diff --git a/services/sync/tests/unit/head_http_server.js b/services/sync/tests/unit/head_http_server.js
index 95df42a0aed8..01678a67f855 100644
--- a/services/sync/tests/unit/head_http_server.js
+++ b/services/sync/tests/unit/head_http_server.js
@@ -199,7 +199,7 @@ ServerCollection.prototype = {
    */
   wbos: function wbos(filter) {
     let os = [];
-    for (let [id, wbo] of Object.entries(this._wbos)) {
+    for (let wbo of Object.values(this._wbos)) {
       if (wbo.payload) {
         os.push(wbo);
       }
@@ -276,7 +276,7 @@ ServerCollection.prototype = {
   count(options) {
     options = options || {};
     let c = 0;
-    for (let [id, wbo] of Object.entries(this._wbos)) {
+    for (let wbo of Object.values(this._wbos)) {
       if (wbo.modified && this._inResultSet(wbo, options)) {
         c++;
       }
@@ -288,7 +288,7 @@ ServerCollection.prototype = {
     let result;
     if (options.full) {
       let data = [];
-      for (let [id, wbo] of Object.entries(this._wbos)) {
+      for (let wbo of Object.values(this._wbos)) {
         // Drop deleted.
         if (wbo.modified && this._inResultSet(wbo, options)) {
           data.push(wbo.get());
@@ -361,7 +361,7 @@ ServerCollection.prototype = {
 
   delete(options) {
     let deleted = [];
-    for (let [id, wbo] of Object.entries(this._wbos)) {
+    for (let wbo of Object.values(this._wbos)) {
       if (this._inResultSet(wbo, options)) {
         this._log.debug("Deleting " + JSON.stringify(wbo));
         deleted.push(wbo.id);
@@ -848,7 +848,7 @@ SyncServer.prototype = {
       throw HTTP_404;
     }
 
-    let [all, version, username, first, rest] = parts;
+    let [, version, username, first, rest] = parts;
     // Doing a float compare of the version allows for us to pretend there was
     // a node-reassignment - eg, we could re-assign from "1.1/user/" to
     // "1.10/user" - this server will then still accept requests with the new
@@ -916,7 +916,7 @@ SyncServer.prototype = {
         this._log.warn("SyncServer: Unknown storage operation " + rest);
         throw HTTP_404;
       }
-      let [all, collection, wboID] = match;
+      let [, collection, wboID] = match;
       let coll = this.getCollection(username, collection);
       switch (req.method) {
         case "GET":
diff --git a/services/sync/tests/unit/test_addon_utils.js b/services/sync/tests/unit/test_addon_utils.js
index a048e10ae32f..ccdce1fb3f80 100644
--- a/services/sync/tests/unit/test_addon_utils.js
+++ b/services/sync/tests/unit/test_addon_utils.js
@@ -23,8 +23,6 @@ function createAndStartHTTPServer(port = HTTP_PORT) {
   try {
     let server = new HttpServer();
 
-    let bootstrap1XPI = ExtensionsTestPath("/addons/test_bootstrap1_1.xpi");
-
     server.registerFile("/search/guid:missing-sourceuri%40tests.mozilla.org",
                         do_get_file("missing-sourceuri.xml"));
 
diff --git a/services/sync/tests/unit/test_addons_reconciler.js b/services/sync/tests/unit/test_addons_reconciler.js
index d93bdfc0380d..d6d278ff3016 100644
--- a/services/sync/tests/unit/test_addons_reconciler.js
+++ b/services/sync/tests/unit/test_addons_reconciler.js
@@ -106,7 +106,6 @@ add_test(function test_uninstall_detection() {
 
   let addon = installAddon("test_bootstrap1_1");
   let id = addon.id;
-  let guid = addon.syncGUID;
 
   reconciler._changes = [];
   uninstallAddon(addon);
diff --git a/services/sync/tests/unit/test_addons_store.js b/services/sync/tests/unit/test_addons_store.js
index 2af7e12ed4fc..f0e009c898b1 100644
--- a/services/sync/tests/unit/test_addons_store.js
+++ b/services/sync/tests/unit/test_addons_store.js
@@ -174,7 +174,7 @@ add_test(function test_ignore_different_appid() {
   do_check_eq(0, failed.length);
 
   let newAddon = getAddonFromAddonManagerByID(addon.id);
-  do_check_false(addon.userDisabled);
+  do_check_false(newAddon.userDisabled);
 
   uninstallAddon(addon);
 
@@ -193,7 +193,7 @@ add_test(function test_ignore_unknown_source() {
   do_check_eq(0, failed.length);
 
   let newAddon = getAddonFromAddonManagerByID(addon.id);
-  do_check_false(addon.userDisabled);
+  do_check_false(newAddon.userDisabled);
 
   uninstallAddon(addon);
 
@@ -431,7 +431,7 @@ add_test(function test_create_bad_install() {
   let guid = Utils.makeGUID();
   let record = createRecordForThisApp(guid, id, true, false);
 
-  let failed = store.applyIncomingBatch([record]);
+  /* let failed = */ store.applyIncomingBatch([record]);
   // This addon had no source URI so was skipped - but it's not treated as
   // failure.
   // XXX - this test isn't testing what we thought it was. Previously the addon
diff --git a/services/sync/tests/unit/test_bookmark_duping.js b/services/sync/tests/unit/test_bookmark_duping.js
index cea77c59755c..66a8134555ba 100644
--- a/services/sync/tests/unit/test_bookmark_duping.js
+++ b/services/sync/tests/unit/test_bookmark_duping.js
@@ -141,7 +141,7 @@ add_task(async function test_dupe_bookmark() {
   try {
     // The parent folder and one bookmark in it.
     let {id: folder1_id, guid: folder1_guid } = createFolder(bms.toolbarFolder, "Folder 1");
-    let {id: bmk1_id, guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
+    let {guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
 
     engine.sync();
 
@@ -192,7 +192,7 @@ add_task(async function test_dupe_reparented_bookmark() {
   try {
     // The parent folder and one bookmark in it.
     let {id: folder1_id, guid: folder1_guid } = createFolder(bms.toolbarFolder, "Folder 1");
-    let {id: bmk1_id, guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
+    let {guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
     // Another parent folder *with the same name*
     let {id: folder2_id, guid: folder2_guid } = createFolder(bms.toolbarFolder, "Folder 1");
 
@@ -258,7 +258,7 @@ add_task(async function test_dupe_reparented_locally_changed_bookmark() {
   try {
     // The parent folder and one bookmark in it.
     let {id: folder1_id, guid: folder1_guid } = createFolder(bms.toolbarFolder, "Folder 1");
-    let {id: bmk1_id, guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
+    let {guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
     // Another parent folder *with the same name*
     let {id: folder2_id, guid: folder2_guid } = createFolder(bms.toolbarFolder, "Folder 1");
 
@@ -335,9 +335,9 @@ add_task(async function test_dupe_reparented_to_earlier_appearing_parent_bookmar
   try {
     // The parent folder and one bookmark in it.
     let {id: folder1_id, guid: folder1_guid } = createFolder(bms.toolbarFolder, "Folder 1");
-    let {id: bmk1_id, guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
+    let {guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
     // One more folder we'll use later.
-    let {id: folder2_id, guid: folder2_guid} = createFolder(bms.toolbarFolder, "A second folder");
+    let {guid: folder2_guid} = createFolder(bms.toolbarFolder, "A second folder");
 
     do_print(`folder1=${folder1_guid}, bmk1=${bmk1_guid} folder2=${folder2_guid}`);
 
@@ -412,9 +412,9 @@ add_task(async function test_dupe_reparented_to_later_appearing_parent_bookmark(
   try {
     // The parent folder and one bookmark in it.
     let {id: folder1_id, guid: folder1_guid } = createFolder(bms.toolbarFolder, "Folder 1");
-    let {id: bmk1_id, guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
+    let {guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
     // One more folder we'll use later.
-    let {id: folder2_id, guid: folder2_guid} = createFolder(bms.toolbarFolder, "A second folder");
+    let {guid: folder2_guid} = createFolder(bms.toolbarFolder, "A second folder");
 
     do_print(`folder1=${folder1_guid}, bmk1=${bmk1_guid} folder2=${folder2_guid}`);
 
@@ -489,9 +489,9 @@ add_task(async function test_dupe_reparented_to_future_arriving_parent_bookmark(
   try {
     // The parent folder and one bookmark in it.
     let {id: folder1_id, guid: folder1_guid } = createFolder(bms.toolbarFolder, "Folder 1");
-    let {id: bmk1_id, guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
+    let {guid: bmk1_guid} = createBookmark(folder1_id, "http://getfirefox.com/", "Get Firefox!");
     // One more folder we'll use later.
-    let {id: folder2_id, guid: folder2_guid} = createFolder(bms.toolbarFolder, "A second folder");
+    let {guid: folder2_guid} = createFolder(bms.toolbarFolder, "A second folder");
 
     do_print(`folder1=${folder1_guid}, bmk1=${bmk1_guid} folder2=${folder2_guid}`);
 
@@ -608,7 +608,7 @@ add_task(async function test_dupe_empty_folder() {
 
   try {
     // The folder we will end up duping away.
-    let {id: folder1_id, guid: folder1_guid } = createFolder(bms.toolbarFolder, "Folder 1");
+    let {guid: folder1_guid } = createFolder(bms.toolbarFolder, "Folder 1");
 
     engine.sync();
 
diff --git a/services/sync/tests/unit/test_bookmark_engine.js b/services/sync/tests/unit/test_bookmark_engine.js
index 7cf8a463b17d..e71b28c8a678 100644
--- a/services/sync/tests/unit/test_bookmark_engine.js
+++ b/services/sync/tests/unit/test_bookmark_engine.js
@@ -49,7 +49,6 @@ add_task(async function test_delete_invalid_roots_from_server() {
 
   let engine  = new BookmarksEngine(Service);
   let store   = engine._store;
-  let tracker = engine._tracker;
   let server = serverForFoo(engine);
   await SyncTestingInfrastructure(server);
 
@@ -106,7 +105,6 @@ add_task(async function test_change_during_sync() {
 
   let engine  = new BookmarksEngine(Service);
   let store   = engine._store;
-  let tracker = engine._tracker;
   let server = serverForFoo(engine);
   await SyncTestingInfrastructure(server);
 
@@ -256,11 +254,9 @@ add_task(async function test_change_during_sync() {
 add_task(async function bad_record_allIDs() {
   let server = new SyncServer();
   server.start();
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   _("Ensure that bad Places queries don't cause an error in getAllIDs.");
-  let engine = new BookmarksEngine(Service);
-  let store = engine._store;
   let badRecordID = PlacesUtils.bookmarks.insertBookmark(
       PlacesUtils.bookmarks.toolbarFolder,
       Utils.makeURI("place:folder=1138"),
@@ -319,10 +315,8 @@ add_task(async function test_processIncoming_error_orderChildren() {
 
     let bmk1_id = PlacesUtils.bookmarks.insertBookmark(
       folder1_id, fxuri, PlacesUtils.bookmarks.DEFAULT_INDEX, "Get Firefox!");
-    let bmk1_guid = store.GUIDForId(bmk1_id);
     let bmk2_id = PlacesUtils.bookmarks.insertBookmark(
       folder1_id, tburi, PlacesUtils.bookmarks.DEFAULT_INDEX, "Get Thunderbird!");
-    let bmk2_guid = store.GUIDForId(bmk2_id);
 
     // Create a server record for folder1 where we flip the order of
     // the children.
diff --git a/services/sync/tests/unit/test_bookmark_record.js b/services/sync/tests/unit/test_bookmark_record.js
index f559f3e4f8e7..1444522c8deb 100644
--- a/services/sync/tests/unit/test_bookmark_record.js
+++ b/services/sync/tests/unit/test_bookmark_record.js
@@ -26,7 +26,6 @@ add_task(async function test_bookmark_record() {
 
   log.info("Creating a record");
 
-  let u = "http://localhost:8080/storage/bookmarks/foo";
   let placesItem = new PlacesItem("bookmarks", "foo", "bookmark");
   let bookmarkItem = prepareBookmarkItem("bookmarks", "foo");
 
diff --git a/services/sync/tests/unit/test_bookmark_smart_bookmarks.js b/services/sync/tests/unit/test_bookmark_smart_bookmarks.js
index 43796f7fa957..c369b59c43ae 100644
--- a/services/sync/tests/unit/test_bookmark_smart_bookmarks.js
+++ b/services/sync/tests/unit/test_bookmark_smart_bookmarks.js
@@ -188,8 +188,6 @@ add_task(async function test_smart_bookmarks_duped() {
   let record = store.createRecord(mostVisitedGUID);
 
   _("Prepare sync.");
-  let collection = server.user("foo").collection("bookmarks");
-
   try {
     engine._syncStartup();
 
diff --git a/services/sync/tests/unit/test_bookmark_tracker.js b/services/sync/tests/unit/test_bookmark_tracker.js
index 696d0688ef37..c39417f60c5f 100644
--- a/services/sync/tests/unit/test_bookmark_tracker.js
+++ b/services/sync/tests/unit/test_bookmark_tracker.js
@@ -129,7 +129,7 @@ var populateTree = async function populate(parentId, ...items) {
 }
 
 async function insertBookmarksToMigrate() {
-  let mozBmk = await PlacesUtils.bookmarks.insert({
+  await PlacesUtils.bookmarks.insert({
     guid: "0gtWTOgYcoJD",
     parentGuid: PlacesUtils.bookmarks.menuGuid,
     url: "https://mozilla.org",
@@ -144,7 +144,7 @@ async function insertBookmarksToMigrate() {
     parentGuid: PlacesUtils.bookmarks.menuGuid,
     url: "http://getthunderbird.com",
   });
-  let bzBmk = await PlacesUtils.bookmarks.insert({
+  await PlacesUtils.bookmarks.insert({
     guid: "YK5Bdq5MIqL6",
     parentGuid: PlacesUtils.bookmarks.menuGuid,
     url: "https://bugzilla.mozilla.org",
@@ -217,7 +217,7 @@ add_task(async function test_batch_tracking() {
 
   PlacesUtils.bookmarks.runInBatchMode({
     runBatched() {
-      let folder = PlacesUtils.bookmarks.createFolder(
+      PlacesUtils.bookmarks.createFolder(
         PlacesUtils.bookmarks.bookmarksMenuFolder,
         "Test Folder", PlacesUtils.bookmarks.DEFAULT_INDEX);
       // We should be tracking the new folder and its parent (and need to jump
@@ -244,7 +244,7 @@ add_task(async function test_nested_batch_tracking() {
 
       PlacesUtils.bookmarks.runInBatchMode({
         runBatched() {
-          let folder = PlacesUtils.bookmarks.createFolder(
+          PlacesUtils.bookmarks.createFolder(
             PlacesUtils.bookmarks.bookmarksMenuFolder,
             "Test Folder", PlacesUtils.bookmarks.DEFAULT_INDEX);
           // We should be tracking the new folder and its parent (and need to jump
@@ -667,7 +667,6 @@ add_task(async function test_onItemKeywordChanged() {
     let folder = PlacesUtils.bookmarks.createFolder(
       PlacesUtils.bookmarks.bookmarksMenuFolder, "Parent",
       PlacesUtils.bookmarks.DEFAULT_INDEX);
-    let folderGUID = engine._store.GUIDForId(folder);
     _("Track changes to keywords");
     let uri = Utils.makeURI("http://getfirefox.com");
     let b = PlacesUtils.bookmarks.insertBookmark(
@@ -803,7 +802,6 @@ add_task(async function test_onItemAnnoChanged() {
     let folder = PlacesUtils.bookmarks.createFolder(
       PlacesUtils.bookmarks.bookmarksMenuFolder, "Parent",
       PlacesUtils.bookmarks.DEFAULT_INDEX);
-    let folderGUID = engine._store.GUIDForId(folder);
     _("Track changes to annos.");
     let b = PlacesUtils.bookmarks.insertBookmark(
       folder, Utils.makeURI("http://getfirefox.com"),
@@ -1074,7 +1072,7 @@ add_task(async function test_async_onItemMoved_update() {
   try {
     await stopTracking();
 
-    let fxBmk = await PlacesUtils.bookmarks.insert({
+    await PlacesUtils.bookmarks.insert({
       type: PlacesUtils.bookmarks.TYPE_BOOKMARK,
       parentGuid: PlacesUtils.bookmarks.menuGuid,
       url: "http://getfirefox.com",
@@ -1301,18 +1299,16 @@ add_task(async function test_treeMoved() {
     let folder2_guid = engine._store.GUIDForId(folder2_id);
 
     // Create a couple of bookmarks in the second folder.
-    let fx_id = PlacesUtils.bookmarks.insertBookmark(
+    PlacesUtils.bookmarks.insertBookmark(
       folder2_id,
       Utils.makeURI("http://getfirefox.com"),
       PlacesUtils.bookmarks.DEFAULT_INDEX,
       "Get Firefox!");
-    let fx_guid = engine._store.GUIDForId(fx_id);
-    let tb_id = PlacesUtils.bookmarks.insertBookmark(
+    PlacesUtils.bookmarks.insertBookmark(
       folder2_id,
       Utils.makeURI("http://getthunderbird.com"),
       PlacesUtils.bookmarks.DEFAULT_INDEX,
       "Get Thunderbird!");
-    let tb_guid = engine._store.GUIDForId(tb_id);
 
     await startTracking();
 
@@ -1332,12 +1328,11 @@ add_task(async function test_onItemDeleted() {
   _("Bookmarks deleted via the synchronous API should be tracked");
 
   try {
-    let fx_id = PlacesUtils.bookmarks.insertBookmark(
+    PlacesUtils.bookmarks.insertBookmark(
       PlacesUtils.bookmarks.bookmarksMenuFolder,
       Utils.makeURI("http://getfirefox.com"),
       PlacesUtils.bookmarks.DEFAULT_INDEX,
       "Get Firefox!");
-    let fx_guid = engine._store.GUIDForId(fx_id);
     let tb_id = PlacesUtils.bookmarks.insertBookmark(
       PlacesUtils.bookmarks.bookmarksMenuFolder,
       Utils.makeURI("http://getthunderbird.com"),
@@ -1370,7 +1365,7 @@ add_task(async function test_async_onItemDeleted() {
       url: "http://getfirefox.com",
       title: "Get Firefox!",
     });
-    let tbBmk = await PlacesUtils.bookmarks.insert({
+    await PlacesUtils.bookmarks.insert({
       type: PlacesUtils.bookmarks.TYPE_BOOKMARK,
       parentGuid: PlacesUtils.bookmarks.menuGuid,
       url: "http://getthunderbird.com",
diff --git a/services/sync/tests/unit/test_browserid_identity.js b/services/sync/tests/unit/test_browserid_identity.js
index fd6ab141167d..b7a9eedcb201 100644
--- a/services/sync/tests/unit/test_browserid_identity.js
+++ b/services/sync/tests/unit/test_browserid_identity.js
@@ -748,7 +748,7 @@ add_task(async function test_signedInUserMissing() {
   _("BrowserIDManager detects getSignedInUser returning incomplete account data");
 
   let browseridManager = new BrowserIDManager();
-  let config = makeIdentityConfig();
+  makeIdentityConfig();
   // Delete stored keys and the key fetch token.
   delete identityConfig.fxaccount.user.kA;
   delete identityConfig.fxaccount.user.kB;
diff --git a/services/sync/tests/unit/test_clients_engine.js b/services/sync/tests/unit/test_clients_engine.js
index 8a95b93e5c1a..ca10fad61fda 100644
--- a/services/sync/tests/unit/test_clients_engine.js
+++ b/services/sync/tests/unit/test_clients_engine.js
@@ -336,7 +336,6 @@ add_test(function test_client_name_change() {
 
   let tracker = engine._tracker;
 
-  let localID = engine.localID;
   let initialName = engine.localName;
 
   Svc.Obs.notify("weave:engine:start-tracking");
@@ -373,7 +372,7 @@ add_test(function test_send_command() {
   let rec = new ClientsRec("clients", remoteId);
 
   store.create(rec);
-  let remoteRecord = store.createRecord(remoteId, "clients");
+  store.createRecord(remoteId, "clients");
 
   let action = "testCommand";
   let args = ["foo", "bar"];
@@ -469,7 +468,6 @@ add_test(function test_command_duplication() {
   engine.sendCommand(action, args, remoteId);
   engine.sendCommand(action, args, remoteId);
 
-  let newRecord = store._remoteClients[remoteId];
   let clientCommands = engine._readCommands()[remoteId];
   equal(clientCommands.length, 1);
 
@@ -776,7 +774,7 @@ add_test(function test_send_uri_to_client_for_display() {
   let rec = new ClientsRec("clients", remoteId);
   rec.name = "remote";
   store.create(rec);
-  let remoteRecord = store.createRecord(remoteId, "clients");
+  store.createRecord(remoteId, "clients");
 
   tracker.clearChangedIDs();
   let initialScore = tracker.score;
@@ -902,7 +900,6 @@ add_task(async function test_merge_commands() {
     crypto: {}
   };
   let server = serverForUsers({"foo": "password"}, contents);
-  let user   = server.user("foo");
 
   await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
@@ -936,8 +933,6 @@ add_task(async function test_merge_commands() {
   }), now - 10));
 
   try {
-    let store = engine._store;
-
     _("First sync. 2 records downloaded.");
     strictEqual(engine.lastRecordUpload, 0);
     engine._sync();
@@ -983,7 +978,6 @@ add_task(async function test_duplicate_remote_commands() {
     crypto: {}
   };
   let server = serverForUsers({"foo": "password"}, contents);
-  let user   = server.user("foo");
 
   await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
@@ -999,8 +993,6 @@ add_task(async function test_duplicate_remote_commands() {
   }), now - 10));
 
   try {
-    let store = engine._store;
-
     _("First sync. 1 record downloaded.");
     strictEqual(engine.lastRecordUpload, 0);
     engine._sync();
@@ -1053,7 +1045,6 @@ add_task(async function test_upload_after_reboot() {
     crypto: {}
   };
   let server = serverForUsers({"foo": "password"}, contents);
-  let user   = server.user("foo");
 
   await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
@@ -1082,8 +1073,6 @@ add_task(async function test_upload_after_reboot() {
   }), now - 10));
 
   try {
-    let store = engine._store;
-
     _("First sync. 2 records downloaded.");
     strictEqual(engine.lastRecordUpload, 0);
     engine._sync();
@@ -1146,7 +1135,6 @@ add_task(async function test_keep_cleared_commands_after_reboot() {
     crypto: {}
   };
   let server = serverForUsers({"foo": "password"}, contents);
-  let user   = server.user("foo");
 
   await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
@@ -1188,8 +1176,6 @@ add_task(async function test_keep_cleared_commands_after_reboot() {
   }), now - 10));
 
   try {
-    let store = engine._store;
-
     _("First sync. Download remote and our record.");
     strictEqual(engine.lastRecordUpload, 0);
 
@@ -1274,7 +1260,6 @@ add_task(async function test_deleted_commands() {
     crypto: {}
   };
   let server = serverForUsers({"foo": "password"}, contents);
-  let user   = server.user("foo");
 
   await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
@@ -1300,8 +1285,6 @@ add_task(async function test_deleted_commands() {
   }), now - 10));
 
   try {
-    let store = engine._store;
-
     _("First sync. 2 records downloaded.");
     engine._sync();
 
@@ -1343,7 +1326,6 @@ add_task(async function test_send_uri_ack() {
     crypto: {}
   };
   let server = serverForUsers({"foo": "password"}, contents);
-  let user   = server.user("foo");
 
   await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
@@ -1411,15 +1393,10 @@ add_task(async function test_command_sync() {
   let server    = serverForUsers({"foo": "password"}, contents);
   await SyncTestingInfrastructure(server);
 
-  let user       = server.user("foo");
   let collection = server.getCollection("foo", "clients");
   let remoteId   = Utils.makeGUID();
   let remoteId2  = Utils.makeGUID();
 
-  function clientWBO(id) {
-    return user.collection("clients").wbo(id);
-  }
-
   _("Create remote client record 1");
   server.insertWBO("foo", "clients", new ServerWBO(remoteId, encryptPayload({
     id: remoteId,
diff --git a/services/sync/tests/unit/test_clients_escape.js b/services/sync/tests/unit/test_clients_escape.js
index 837afc7a49a5..d755364a14dc 100644
--- a/services/sync/tests/unit/test_clients_escape.js
+++ b/services/sync/tests/unit/test_clients_escape.js
@@ -11,10 +11,6 @@ add_task(async function test_clients_escape() {
   _("Set up test fixtures.");
 
   await configureIdentity();
-  let baseUri = "http://fakebase/1.1/foo/storage/";
-  let pubUri = baseUri + "keys/pubkey";
-  let privUri = baseUri + "keys/privkey";
-
   let keyBundle = Service.identity.syncKeyBundle;
 
   let engine = Service.clientsEngine;
diff --git a/services/sync/tests/unit/test_collection_getBatched.js b/services/sync/tests/unit/test_collection_getBatched.js
index c6523d497a15..aa92b6f07629 100644
--- a/services/sync/tests/unit/test_collection_getBatched.js
+++ b/services/sync/tests/unit/test_collection_getBatched.js
@@ -126,13 +126,13 @@ add_test(function test_total_limit() {
   const recordLimit = 11;
   const batchSize = 2;
   const lastModified = "111111";
-  let { records, responses, requests, coll } = get_test_collection_info({
+  let { records, requests, coll } = get_test_collection_info({
     totalRecords,
     batchSize,
     lastModified,
   });
   coll.limit = recordLimit;
-  let response = coll.getBatched(batchSize);
+  coll.getBatched(batchSize);
 
   equal(requests.length, Math.ceil(recordLimit / batchSize));
   equal(records.length, recordLimit);
@@ -180,7 +180,7 @@ add_test(function test_get_throws() {
   const totalRecords = 11;
   const batchSize = 2;
   const lastModified = "111111";
-  let { records, responses, requests, coll } = get_test_collection_info({
+  let { records, requests, coll } = get_test_collection_info({
     totalRecords,
     batchSize,
     lastModified,
diff --git a/services/sync/tests/unit/test_corrupt_keys.js b/services/sync/tests/unit/test_corrupt_keys.js
index 0dbb07bed119..f3ddc56f9ea5 100644
--- a/services/sync/tests/unit/test_corrupt_keys.js
+++ b/services/sync/tests/unit/test_corrupt_keys.js
@@ -90,8 +90,6 @@ add_task(async function test_locally_changed_keys() {
     _("Tabs modified: " + johndoe.modified("tabs"));
     do_check_true(johndoe.modified("tabs") > 0);
 
-    let coll_modified = Service.collectionKeys.lastModified;
-
     // Let's create some server side history records.
     let liveKeys = Service.collectionKeys.keyForCollection("history");
     _("Keys now: " + liveKeys.keyPair);
@@ -144,7 +142,6 @@ add_task(async function test_locally_changed_keys() {
     _("Keys now: " + Service.collectionKeys.keyForCollection("history").keyPair);
 
     // And look! We downloaded history!
-    let store = Service.engineManager.get("history")._store;
     do_check_true(await promiseIsURIVisited("http://foo/bar?record-no--0"));
     do_check_true(await promiseIsURIVisited("http://foo/bar?record-no--1"));
     do_check_true(await promiseIsURIVisited("http://foo/bar?record-no--2"));
@@ -202,7 +199,6 @@ add_task(async function test_locally_changed_keys() {
 });
 
 function run_test() {
-  let logger = Log.repository.rootLogger;
   Log.repository.rootLogger.addAppender(new Log.DumpAppender());
   validate_all_future_pings();
 
diff --git a/services/sync/tests/unit/test_errorhandler_2.js b/services/sync/tests/unit/test_errorhandler_2.js
index d9bc285c7c77..8275fc6d7b6b 100644
--- a/services/sync/tests/unit/test_errorhandler_2.js
+++ b/services/sync/tests/unit/test_errorhandler_2.js
@@ -900,7 +900,6 @@ add_task(async function test_engine_applyFailed() {
     Svc.Obs.notify("weave:engine:sync:applied", {newFailed:1}, "catapult");
   };
 
-  let log = Log.repository.getLogger("Sync.ErrorHandler");
   Svc.Prefs.set("log.appender.file.logOnError", true);
 
   let promiseObserved = promiseOneObserver("weave:service:reset-file-log");
diff --git a/services/sync/tests/unit/test_errorhandler_filelog.js b/services/sync/tests/unit/test_errorhandler_filelog.js
index 76fdf7b5baf6..8e2a405bf5c8 100644
--- a/services/sync/tests/unit/test_errorhandler_filelog.js
+++ b/services/sync/tests/unit/test_errorhandler_filelog.js
@@ -273,8 +273,6 @@ add_test(function test_login_error_logOnError_true() {
 add_test(function test_errorLog_dumpAddons() {
   Svc.Prefs.set("log.appender.file.logOnError", true);
 
-  let log = Log.repository.getLogger("Sync.Test.FileLog");
-
   // We need to wait until the log cleanup started by this test is complete
   // or the next test will fail as it is ongoing.
   Svc.Obs.add("services-tests:common:log-manager:cleanup-logs", function onCleanupLogs() {
diff --git a/services/sync/tests/unit/test_errorhandler_sync_checkServerError.js b/services/sync/tests/unit/test_errorhandler_sync_checkServerError.js
index 561c55f4b82a..1840f1bdf8ee 100644
--- a/services/sync/tests/unit/test_errorhandler_sync_checkServerError.js
+++ b/services/sync/tests/unit/test_errorhandler_sync_checkServerError.js
@@ -30,7 +30,6 @@ CatapultEngine.prototype = {
 function sync_httpd_setup() {
   let collectionsHelper = track_collections_helper();
   let upd = collectionsHelper.with_updated_collection;
-  let collections = collectionsHelper.collections;
 
   let catapultEngine = engineManager.get("catapult");
   let engines        = {catapult: {version: catapultEngine.version,
diff --git a/services/sync/tests/unit/test_forms_store.js b/services/sync/tests/unit/test_forms_store.js
index 6963df1c0b00..78fa6755661c 100644
--- a/services/sync/tests/unit/test_forms_store.js
+++ b/services/sync/tests/unit/test_forms_store.js
@@ -8,7 +8,6 @@ Cu.import("resource://services-sync/util.js");
 Cu.import("resource://gre/modules/Services.jsm");
 
 function run_test() {
-  let baseuri = "http://fake/uri/";
   let engine = new FormEngine(Service);
   let store = engine._store;
 
@@ -18,7 +17,7 @@ function run_test() {
 
   _("Remove any existing entries");
   store.wipe();
-  for (let id in store.getAllIDs()) {
+  if (store.getAllIDs().length) {
     do_throw("Shouldn't get any ids!");
   }
 
@@ -55,7 +54,7 @@ function run_test() {
 
   _("Remove all entries");
   store.wipe();
-  for (let id in store.getAllIDs()) {
+  if (store.getAllIDs().length) {
     do_throw("Shouldn't get any ids!");
   }
 
@@ -83,7 +82,7 @@ function run_test() {
   store.remove({
     id: "newid"
   });
-  for (let id in store.getAllIDs()) {
+  if (store.getAllIDs().length) {
     do_throw("Shouldn't get any ids!");
   }
 
@@ -91,7 +90,7 @@ function run_test() {
   store.remove({
     id: "newid"
   });
-  for (let id in store.getAllIDs()) {
+  if (store.getAllIDs().length) {
     do_throw("Shouldn't get any ids!");
   }
 
@@ -114,7 +113,7 @@ function run_test() {
   toDelete.id = id;
   toDelete.deleted = true;
   applyEnsureNoFailures([toDelete]);
-  for (let id in store.getAllIDs()) {
+  if (store.getAllIDs().length) {
     do_throw("Shouldn't get any ids!");
   }
 
@@ -127,7 +126,7 @@ function run_test() {
 
   store.wipe();
 
-  for (let id in store.getAllIDs()) {
+  if (store.getAllIDs().length) {
     do_throw("Shouldn't get any ids!");
   }
 
@@ -135,7 +134,7 @@ function run_test() {
   Services.prefs.setBoolPref("browser.formfill.enable", false);
   try {
     // a search
-    for (let id in store.getAllIDs()) {
+    if (store.getAllIDs().length) {
       do_throw("Shouldn't get any ids!");
     }
     // an update.
diff --git a/services/sync/tests/unit/test_fxa_migration.js b/services/sync/tests/unit/test_fxa_migration.js
index 606cdf51edd3..991d0e891c5b 100644
--- a/services/sync/tests/unit/test_fxa_migration.js
+++ b/services/sync/tests/unit/test_fxa_migration.js
@@ -72,7 +72,7 @@ add_task(async function testMigrationUnlinks() {
   });
 
   // Arrange for a legacy sync user.
-  let [engine, server] = configureLegacySync();
+  configureLegacySync();
 
   // Start a sync - this will cause an EOL notification which the migrator's
   // observer will notice.
diff --git a/services/sync/tests/unit/test_history_tracker.js b/services/sync/tests/unit/test_history_tracker.js
index fb5fe5eb2f43..5948586fa02f 100644
--- a/services/sync/tests/unit/test_history_tracker.js
+++ b/services/sync/tests/unit/test_history_tracker.js
@@ -209,8 +209,6 @@ add_task(async function test_track_delete() {
 
 add_task(async function test_dont_track_expiration() {
   _("Expirations are not tracked.");
-  let uriToExpire = await addVisit("to_expire");
-  let guidToExpire = engine._store.GUIDForUri(uriToExpire);
   let uriToRemove = await addVisit("to_remove");
   let guidToRemove = engine._store.GUIDForUri(uriToRemove);
 
diff --git a/services/sync/tests/unit/test_hmac_error.js b/services/sync/tests/unit/test_hmac_error.js
index 83c08db89032..6aa91d91576f 100644
--- a/services/sync/tests/unit/test_hmac_error.js
+++ b/services/sync/tests/unit/test_hmac_error.js
@@ -65,7 +65,6 @@ add_task(async function hmac_error_during_404() {
 
   let collectionsHelper = track_collections_helper();
   let upd = collectionsHelper.with_updated_collection;
-  let collections = collectionsHelper.collections;
   let handlers = {
     "/1.1/foo/info/collections": collectionsHelper.handler,
     "/1.1/foo/storage/meta/global": upd("meta", global.handler()),
diff --git a/services/sync/tests/unit/test_httpd_sync_server.js b/services/sync/tests/unit/test_httpd_sync_server.js
index ba2893e65372..75e24c15f6b0 100644
--- a/services/sync/tests/unit/test_httpd_sync_server.js
+++ b/services/sync/tests/unit/test_httpd_sync_server.js
@@ -57,8 +57,8 @@ add_test(function test_url_parsing() {
   do_check_eq(rest, undefined);
 
   parts = server.storageRE.exec("storage");
-  let storage, collection, id;
-  [all, storage, collection, id] = parts;
+  let collection;
+  [all, , collection, ] = parts;
   do_check_eq(all, "storage");
   do_check_eq(collection, undefined);
 
diff --git a/services/sync/tests/unit/test_keys.js b/services/sync/tests/unit/test_keys.js
index c86e589676ca..f6ffc8a923fe 100644
--- a/services/sync/tests/unit/test_keys.js
+++ b/services/sync/tests/unit/test_keys.js
@@ -22,7 +22,6 @@ function do_check_keypair_eq(a, b) {
 }
 
 function test_time_keyFromString(iterations) {
-  let k;
   let o;
   let b = new BulkKeyBundle("dummy");
   let d = Utils.decodeKeyBase32("ababcdefabcdefabcdefabcdef");
diff --git a/services/sync/tests/unit/test_password_store.js b/services/sync/tests/unit/test_password_store.js
index f21fbb95f3ea..4cff7ddc08e1 100644
--- a/services/sync/tests/unit/test_password_store.js
+++ b/services/sync/tests/unit/test_password_store.js
@@ -119,7 +119,6 @@ function test_apply_same_record_with_different_times() {
   // The following record is going to be inserted multiple times in the store
   // and it needs to be found there. Then its timestamps are going to be
   // compared to the expected values.
-  var timePasswordChanged = 100;
   timePasswordChanged = changePassword("A", "http://a.tn", "password", 1, 100,
                                        100, 100, timePasswordChanged, true);
   timePasswordChanged = changePassword("A", "http://a.tn", "password", 1, 100,
diff --git a/services/sync/tests/unit/test_records_crypto.js b/services/sync/tests/unit/test_records_crypto.js
index d4953d2a2cdf..96db8b63bf7a 100644
--- a/services/sync/tests/unit/test_records_crypto.js
+++ b/services/sync/tests/unit/test_records_crypto.js
@@ -43,7 +43,6 @@ add_task(async function test_records_crypto() {
 
     log.info("Creating a record");
 
-    let cryptoUri = "http://localhost:8080/crypto/steam";
     cryptoWrap = prepareCryptoWrap("steam", "resource");
 
     log.info("cryptoWrap: " + cryptoWrap.toString());
@@ -107,7 +106,6 @@ add_task(async function test_records_crypto() {
     // Checking per-collection keys and default key handling.
 
     generateNewKeys(Service.collectionKeys);
-    let bu = "http://localhost:8080/storage/bookmarks/foo";
     let bookmarkItem = prepareCryptoWrap("bookmarks", "foo");
     bookmarkItem.encrypt(Service.collectionKeys.keyForCollection("bookmarks"));
     log.info("Ciphertext is " + bookmarkItem.ciphertext);
diff --git a/services/sync/tests/unit/test_resource.js b/services/sync/tests/unit/test_resource.js
index 607d7f4bf237..62231073ed28 100644
--- a/services/sync/tests/unit/test_resource.js
+++ b/services/sync/tests/unit/test_resource.js
@@ -429,7 +429,6 @@ function run_test() {
     Services.io.newURI("::::::::");
   };
   res18._onProgress = onProgress;
-  let oldWarn = res18._log.warn;
   let warnings = [];
   res18._log.warn = function(msg) { warnings.push(msg) };
   error = undefined;
diff --git a/services/sync/tests/unit/test_resource_async.js b/services/sync/tests/unit/test_resource_async.js
index 25b87ce03df3..6dd3d9d09a1d 100644
--- a/services/sync/tests/unit/test_resource_async.js
+++ b/services/sync/tests/unit/test_resource_async.js
@@ -701,12 +701,6 @@ add_test(function test_uri_construction() {
 });
 
 add_test(function test_not_sending_cookie() {
-  function handler(metadata, response) {
-    let body = "COOKIE!";
-    response.setStatusLine(metadata.httpVersion, 200, "OK");
-    response.bodyOutputStream.write(body, body.length);
-    do_check_false(metadata.hasHeader("Cookie"));
-  }
   let cookieSer = Cc["@mozilla.org/cookieService;1"]
                     .getService(Ci.nsICookieService);
   let uri = CommonUtils.makeURI(server.baseURI);
diff --git a/services/sync/tests/unit/test_service_detect_upgrade.js b/services/sync/tests/unit/test_service_detect_upgrade.js
index 0fde13f198fc..916b6086cc9c 100644
--- a/services/sync/tests/unit/test_service_detect_upgrade.js
+++ b/services/sync/tests/unit/test_service_detect_upgrade.js
@@ -194,7 +194,6 @@ add_test(function v5_upgrade() {
   // Tracking info/collections.
   let collectionsHelper = track_collections_helper();
   let upd = collectionsHelper.with_updated_collection;
-  let collections = collectionsHelper.collections;
 
   let keysWBO = new ServerWBO("keys");
   let bulkWBO = new ServerWBO("bulk");
@@ -288,7 +287,6 @@ add_test(function v5_upgrade() {
 });
 
 function run_test() {
-  let logger = Log.repository.rootLogger;
   Log.repository.rootLogger.addAppender(new Log.DumpAppender());
 
   run_next_test();
diff --git a/services/sync/tests/unit/test_service_getStorageInfo.js b/services/sync/tests/unit/test_service_getStorageInfo.js
index 56c0f4312201..a5e9d6c50d5f 100644
--- a/services/sync/tests/unit/test_service_getStorageInfo.js
+++ b/services/sync/tests/unit/test_service_getStorageInfo.js
@@ -73,7 +73,7 @@ add_test(function test_http_error() {
   Service.serverURL = server.baseURI + "/";
   Service.clusterURL = server.baseURI + "/";
 
-  let request = Service.getStorageInfo(INFO_COLLECTIONS, function(error, info) {
+  Service.getStorageInfo(INFO_COLLECTIONS, function(error, info) {
     do_check_eq(error.status, 500);
     do_check_eq(info, null);
     server.stop(run_next_test);
@@ -86,7 +86,7 @@ add_test(function test_invalid_json() {
   Service.serverURL = server.baseURI + "/";
   Service.clusterURL = server.baseURI + "/";
 
-  let request = Service.getStorageInfo(INFO_COLLECTIONS, function(error, info) {
+  Service.getStorageInfo(INFO_COLLECTIONS, function(error, info) {
     do_check_eq(error.name, "SyntaxError");
     do_check_eq(info, null);
     server.stop(run_next_test);
diff --git a/services/sync/tests/unit/test_service_login.js b/services/sync/tests/unit/test_service_login.js
index d42b45d5598b..4f228eaca711 100644
--- a/services/sync/tests/unit/test_service_login.js
+++ b/services/sync/tests/unit/test_service_login.js
@@ -23,7 +23,6 @@ function login_handling(handler) {
 }
 
 function run_test() {
-  let logger = Log.repository.rootLogger;
   Log.repository.rootLogger.addAppender(new Log.DumpAppender());
 
   run_next_test();
@@ -45,10 +44,8 @@ add_test(function test_offline() {
 function setup() {
   let janeHelper = track_collections_helper();
   let janeU      = janeHelper.with_updated_collection;
-  let janeColls  = janeHelper.collections;
   let johnHelper = track_collections_helper();
   let johnU      = johnHelper.with_updated_collection;
-  let johnColls  = johnHelper.collections;
 
   let server = httpd_setup({
     "/1.1/johndoe/info/collections": login_handling(johnHelper.handler),
@@ -157,7 +154,6 @@ add_test(function test_login_on_sync() {
     Service.login = oldLogin;
 
     // Stub mpLocked.
-    let mpLockedF = Utils.mpLocked;
     let mpLocked = true;
     Utils.mpLocked = () => mpLocked;
 
@@ -209,9 +205,6 @@ add_test(function test_login_on_sync() {
                              throw "User canceled Master Password entry";
                            });
 
-    let oldClearSyncTriggers = Service.scheduler.clearSyncTriggers;
-    let oldLockedSync = Service._lockedSync;
-
     let cSTCalled = false;
     let lockedSyncCalled = false;
 
diff --git a/services/sync/tests/unit/test_service_passwordUTF8.js b/services/sync/tests/unit/test_service_passwordUTF8.js
index fc74b6b53401..a25020b4aeae 100644
--- a/services/sync/tests/unit/test_service_passwordUTF8.js
+++ b/services/sync/tests/unit/test_service_passwordUTF8.js
@@ -56,7 +56,6 @@ function run_test() {
   initTestLogging("Trace");
   let collectionsHelper = track_collections_helper();
   let upd = collectionsHelper.with_updated_collection;
-  let collections = collectionsHelper.collections;
 
   ensureLegacyIdentityManager();
 
diff --git a/services/sync/tests/unit/test_service_sync_401.js b/services/sync/tests/unit/test_service_sync_401.js
index e83c001ba3e0..c383140197ac 100644
--- a/services/sync/tests/unit/test_service_sync_401.js
+++ b/services/sync/tests/unit/test_service_sync_401.js
@@ -21,12 +21,10 @@ function login_handling(handler) {
 }
 
 add_task(async function run_test() {
-  let logger = Log.repository.rootLogger;
   Log.repository.rootLogger.addAppender(new Log.DumpAppender());
 
   let collectionsHelper = track_collections_helper();
   let upd = collectionsHelper.with_updated_collection;
-  let collections = collectionsHelper.collections;
 
   let server = httpd_setup({
     "/1.1/johndoe/storage/crypto/keys": upd("crypto", new ServerWBO("keys").handler()),
diff --git a/services/sync/tests/unit/test_service_sync_remoteSetup.js b/services/sync/tests/unit/test_service_sync_remoteSetup.js
index 75f3be2e6a04..ace57850b510 100644
--- a/services/sync/tests/unit/test_service_sync_remoteSetup.js
+++ b/services/sync/tests/unit/test_service_sync_remoteSetup.js
@@ -11,10 +11,8 @@ Cu.import("resource://testing-common/services/sync/utils.js");
 
 function run_test() {
   validate_all_future_pings();
-  let logger = Log.repository.rootLogger;
   Log.repository.rootLogger.addAppender(new Log.DumpAppender());
 
-  let guidSvc = new FakeGUIDService();
   let clients = new ServerCollection();
   let meta_global = new ServerWBO("global");
 
@@ -55,7 +53,6 @@ function run_test() {
   }
 
   const GLOBAL_PATH = "/1.1/johndoe/storage/meta/global";
-  const INFO_PATH = "/1.1/johndoe/info/collections";
 
   let handlers = {
     "/1.1/johndoe/storage": storageHandler,
@@ -160,7 +157,6 @@ function run_test() {
     metaColl.delete({});
 
     _("Do an initial sync.");
-    let beforeSync = Date.now() / 1000;
     Service.sync();
 
     _("Checking that remoteSetup returns true.");
diff --git a/services/sync/tests/unit/test_service_sync_updateEnabledEngines.js b/services/sync/tests/unit/test_service_sync_updateEnabledEngines.js
index bf90296e5c35..f5291aa55f0b 100644
--- a/services/sync/tests/unit/test_service_sync_updateEnabledEngines.js
+++ b/services/sync/tests/unit/test_service_sync_updateEnabledEngines.js
@@ -199,7 +199,6 @@ add_task(async function test_disabledLocally_wipe503() {
     engines: {steam: {syncID: engine.syncID,
                       version: engine.version}}
   });
-  let steamCollection = new ServerWBO("steam", PAYLOAD);
 
   function service_unavailable(request, response) {
     let body = "Service Unavailable";
diff --git a/services/sync/tests/unit/test_service_verifyLogin.js b/services/sync/tests/unit/test_service_verifyLogin.js
index 307cd8442197..8f4a4e7766f2 100644
--- a/services/sync/tests/unit/test_service_verifyLogin.js
+++ b/services/sync/tests/unit/test_service_verifyLogin.js
@@ -27,7 +27,6 @@ function service_unavailable(request, response) {
 }
 
 function run_test() {
-  let logger = Log.repository.rootLogger;
   Log.repository.rootLogger.addAppender(new Log.DumpAppender());
 
   ensureLegacyIdentityManager();
@@ -35,7 +34,6 @@ function run_test() {
   Services.logins.removeAllLogins();
   let johnHelper = track_collections_helper();
   let johnU      = johnHelper.with_updated_collection;
-  let johnColls  = johnHelper.collections;
 
   do_test_pending();
 
diff --git a/services/sync/tests/unit/test_service_wipeServer.js b/services/sync/tests/unit/test_service_wipeServer.js
index 87f1b429f11a..781d2b900396 100644
--- a/services/sync/tests/unit/test_service_wipeServer.js
+++ b/services/sync/tests/unit/test_service_wipeServer.js
@@ -32,8 +32,6 @@ FakeCollection.prototype = {
 };
 
 async function setUpTestFixtures(server) {
-  let cryptoService = new FakeCryptoService();
-
   Service.serverURL = server.baseURI + "/";
   Service.clusterURL = server.baseURI + "/";
 
diff --git a/services/sync/tests/unit/test_status.js b/services/sync/tests/unit/test_status.js
index ea6a099361bc..eb783bc51576 100644
--- a/services/sync/tests/unit/test_status.js
+++ b/services/sync/tests/unit/test_status.js
@@ -11,7 +11,7 @@ function run_test() {
   do_check_eq(Status.service, STATUS_OK);
   do_check_eq(Status.sync, SYNC_SUCCEEDED);
   do_check_eq(Status.login, LOGIN_SUCCEEDED);
-  for (let name in Status.engines) {
+  if (Status.engines.length) {
     do_throw("Status.engines should be empty.");
   }
   do_check_eq(Status.partial, false);
diff --git a/services/sync/tests/unit/test_syncengine.js b/services/sync/tests/unit/test_syncengine.js
index 86e0815d2adf..072620552806 100644
--- a/services/sync/tests/unit/test_syncengine.js
+++ b/services/sync/tests/unit/test_syncengine.js
@@ -15,7 +15,7 @@ var server = httpd_setup({});
 
 add_task(async function test_url_attributes() {
   _("SyncEngine url attributes");
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   Service.clusterURL = "https://cluster/1.1/foo/";
   let engine = makeSteamEngine();
   try {
@@ -29,7 +29,7 @@ add_task(async function test_url_attributes() {
 
 add_task(async function test_syncID() {
   _("SyncEngine.syncID corresponds to preference");
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   let engine = makeSteamEngine();
   try {
     // Ensure pristine environment
@@ -49,7 +49,7 @@ add_task(async function test_syncID() {
 
 add_task(async function test_lastSync() {
   _("SyncEngine.lastSync and SyncEngine.lastSyncLocal correspond to preferences");
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   let engine = makeSteamEngine();
   try {
     // Ensure pristine environment
@@ -139,7 +139,7 @@ add_task(async function test_previousFailed() {
 
 add_task(async function test_resetClient() {
   _("SyncEngine.resetClient resets lastSync and toFetch");
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   let engine = makeSteamEngine();
   try {
     // Ensure pristine environment
@@ -171,7 +171,7 @@ add_task(async function test_wipeServer() {
   let server = httpd_setup({
     "/1.1/foo/storage/steam": steamCollection.handler()
   });
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   do_test_pending();
 
   try {
diff --git a/services/sync/tests/unit/test_syncengine_sync.js b/services/sync/tests/unit/test_syncengine_sync.js
index 96dfd2878e5b..a22cce2028a6 100644
--- a/services/sync/tests/unit/test_syncengine_sync.js
+++ b/services/sync/tests/unit/test_syncengine_sync.js
@@ -97,7 +97,7 @@ add_task(async function test_syncStartup_emptyOrOutdatedGlobalsResetsSync() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   Service.identity.username = "foo";
 
   let engine = makeRotaryEngine();
@@ -141,7 +141,7 @@ add_task(async function test_syncStartup_serverHasNewerVersion() {
       "/1.1/foo/storage/meta/global": global.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   Service.identity.username = "foo";
 
   let engine = makeRotaryEngine();
@@ -167,7 +167,7 @@ add_task(async function test_syncStartup_syncIDMismatchResetsClient() {
   _("SyncEngine._syncStartup resets sync if syncIDs don't match");
 
   let server = sync_httpd_setup({});
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   Service.identity.username = "foo";
 
   // global record with a different syncID than our engine has
@@ -207,7 +207,7 @@ add_task(async function test_processIncoming_emptyServer() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   Service.identity.username = "foo";
 
   let engine = makeRotaryEngine();
@@ -246,7 +246,7 @@ add_task(async function test_processIncoming_createFromServer() {
       "/1.1/foo/storage/rotary/scotsman": collection.wbo("scotsman").handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   Service.identity.username = "foo";
 
   generateNewKeys(Service.collectionKeys);
@@ -331,7 +331,7 @@ add_task(async function test_processIncoming_reconcile() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   Service.identity.username = "foo";
 
   let engine = makeRotaryEngine();
@@ -633,7 +633,7 @@ add_task(async function test_processIncoming_mobile_batchSize() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let engine = makeRotaryEngine();
   let meta_global = Service.recordManager.set(engine.metaURL,
@@ -708,7 +708,7 @@ add_task(async function test_processIncoming_store_toFetch() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
@@ -720,11 +720,9 @@ add_task(async function test_processIncoming_store_toFetch() {
     do_check_eq(engine.lastSync, 0);
     do_check_empty(engine._store.items);
 
-    let error;
     try {
       await sync_engine_and_validate_telem(engine, true);
     } catch (ex) {
-      error = ex;
     }
 
     // Only the first two batches have been applied.
@@ -781,7 +779,7 @@ add_task(async function test_processIncoming_resume_toFetch() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
@@ -839,7 +837,7 @@ add_task(async function test_processIncoming_applyIncomingBatchSize_smaller() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
@@ -895,7 +893,7 @@ add_task(async function test_processIncoming_applyIncomingBatchSize_multiple() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
@@ -947,7 +945,7 @@ add_task(async function test_processIncoming_notify_count() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
@@ -1037,7 +1035,7 @@ add_task(async function test_processIncoming_previousFailed() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
@@ -1153,7 +1151,7 @@ add_task(async function test_processIncoming_failed_records() {
       "/1.1/foo/storage/rotary": recording_handler(collection)
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
@@ -1266,7 +1264,7 @@ add_task(async function test_processIncoming_decrypt_failed() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
@@ -1323,7 +1321,7 @@ add_task(async function test_uploadOutgoing_toEmptyServer() {
       "/1.1/foo/storage/rotary/scotsman": collection.wbo("scotsman").handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
 
   let engine = makeRotaryEngine();
@@ -1379,7 +1377,7 @@ add_task(async function test_uploadOutgoing_huge() {
       "/1.1/foo/storage/rotary/flying": collection.wbo("flying").handler(),
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
 
   let engine = makeRotaryEngine();
@@ -1428,7 +1426,7 @@ add_task(async function test_uploadOutgoing_failed() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let engine = makeRotaryEngine();
   engine.lastSync = 123; // needs to be non-zero so that tracker is queried
@@ -1523,8 +1521,7 @@ add_task(async function test_uploadOutgoing_MAX_UPLOAD_RECORDS() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
-
+  await SyncTestingInfrastructure(server);
   try {
 
     // Confirm initial environment.
@@ -1568,7 +1565,7 @@ add_task(async function test_uploadOutgoing_largeRecords() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   try {
     engine._syncStartup();
@@ -1590,7 +1587,7 @@ add_task(async function test_syncFinish_noDelete() {
 
   let server = httpd_setup({});
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   let engine = makeRotaryEngine();
   engine._delete = {}; // Nothing to delete
   engine._tracker.score = 100;
@@ -1620,7 +1617,7 @@ add_task(async function test_syncFinish_deleteByIds() {
   let server = httpd_setup({
       "/1.1/foo/storage/rotary": collection.handler()
   });
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let engine = makeRotaryEngine();
   try {
@@ -1671,7 +1668,7 @@ add_task(async function test_syncFinish_deleteLotsInBatches() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let engine = makeRotaryEngine();
   try {
@@ -1722,7 +1719,7 @@ add_task(async function test_sync_partialUpload() {
   let server = sync_httpd_setup({
       "/1.1/foo/storage/rotary": collection.handler()
   });
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   generateNewKeys(Service.collectionKeys);
 
   let engine = makeRotaryEngine();
@@ -1804,7 +1801,7 @@ add_task(async function test_canDecrypt_noCryptoKeys() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   let engine = makeRotaryEngine();
   try {
 
@@ -1830,7 +1827,7 @@ add_task(async function test_canDecrypt_true() {
       "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   let engine = makeRotaryEngine();
   try {
 
@@ -1861,7 +1858,7 @@ add_task(async function test_syncapplied_observer() {
     "/1.1/foo/storage/rotary": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
 
   let meta_global = Service.recordManager.set(engine.metaURL,
                                               new WBORecord(engine.metaURL));
diff --git a/services/sync/tests/unit/test_tab_engine.js b/services/sync/tests/unit/test_tab_engine.js
index d9badd745a73..3218a272eeeb 100644
--- a/services/sync/tests/unit/test_tab_engine.js
+++ b/services/sync/tests/unit/test_tab_engine.js
@@ -78,7 +78,7 @@ add_task(async function test_tab_engine_skips_incoming_local_record() {
       "/1.1/foo/storage/tabs": collection.handler()
   });
 
-  let syncTesting = await SyncTestingInfrastructure(server);
+  await SyncTestingInfrastructure(server);
   Service.identity.username = "foo";
 
   let meta_global = Service.recordManager.set(engine.metaURL,
@@ -105,7 +105,7 @@ add_task(async function test_tab_engine_skips_incoming_local_record() {
 });
 
 add_test(function test_reconcile() {
-  let [engine, store] = getMocks();
+  let [engine, ] = getMocks();
 
   _("Setup engine for reconciling");
   engine._syncStartup();
diff --git a/services/sync/tests/unit/test_tab_store.js b/services/sync/tests/unit/test_tab_store.js
index 86844bd7aaa3..5ba1d281d5fc 100644
--- a/services/sync/tests/unit/test_tab_store.js
+++ b/services/sync/tests/unit/test_tab_store.js
@@ -93,8 +93,6 @@ function test_createRecord() {
   store.shouldSkipWindow = mockShouldSkipWindow;
   store.getWindowEnumerator = mockGetWindowEnumerator.bind(this, "http://foo.com", 1, 1);
 
-  let tabs = store.getAllTabs();
-  let tabsize = JSON.stringify(tabs[0]).length;
   let numtabs = Math.ceil(20000. / 77.);
 
   store.getWindowEnumerator = mockGetWindowEnumerator.bind(this, "http://foo.com", 1, 1);
diff --git a/services/sync/tests/unit/test_telemetry.js b/services/sync/tests/unit/test_telemetry.js
index fa208f8c5c51..088a8ec6376d 100644
--- a/services/sync/tests/unit/test_telemetry.js
+++ b/services/sync/tests/unit/test_telemetry.js
@@ -160,15 +160,10 @@ add_task(async function test_uploading() {
 
   let parent = PlacesUtils.toolbarFolderId;
   let uri = Utils.makeURI("http://getfirefox.com/");
-  let title = "Get Firefox";
 
   let bmk_id = PlacesUtils.bookmarks.insertBookmark(parent, uri,
     PlacesUtils.bookmarks.DEFAULT_INDEX, "Get Firefox!");
 
-  let guid = store.GUIDForId(bmk_id);
-  let record = store.createRecord(guid);
-
-  let collection = server.user("foo").collection("bookmarks");
   try {
     let ping = await sync_engine_and_validate_telem(engine, false);
     ok(!!ping);
@@ -338,7 +333,6 @@ add_task(async function test_generic_engine_fail() {
   Service.engineManager.register(SteamEngine);
   let engine = Service.engineManager.get("steam");
   engine.enabled = true;
-  let store  = engine._store;
   let server = serverForUsers({"foo": "password"}, {
     meta: {global: {engines: {steam: {version: engine.version,
                                       syncID: engine.syncID}}}},
@@ -367,7 +361,6 @@ add_task(async function test_engine_fail_ioerror() {
   Service.engineManager.register(SteamEngine);
   let engine = Service.engineManager.get("steam");
   engine.enabled = true;
-  let store  = engine._store;
   let server = serverForUsers({"foo": "password"}, {
     meta: {global: {engines: {steam: {version: engine.version,
                                       syncID: engine.syncID}}}},
@@ -405,7 +398,6 @@ add_task(async function test_initial_sync_engines() {
   Service.engineManager.register(SteamEngine);
   let engine = Service.engineManager.get("steam");
   engine.enabled = true;
-  let store  = engine._store;
   let engines = {};
   // These are the only ones who actually have things to sync at startup.
   let engineNames = ["clients", "bookmarks", "prefs", "tabs"];
@@ -444,7 +436,6 @@ add_task(async function test_nserror() {
   Service.engineManager.register(SteamEngine);
   let engine = Service.engineManager.get("steam");
   engine.enabled = true;
-  let store  = engine._store;
   let server = serverForUsers({"foo": "password"}, {
     meta: {global: {engines: {steam: {version: engine.version,
                                       syncID: engine.syncID}}}},
@@ -520,7 +511,6 @@ add_task(async function test_no_foreign_engines_in_error_ping() {
   Service.engineManager.register(BogusEngine);
   let engine = Service.engineManager.get("bogus");
   engine.enabled = true;
-  let store  = engine._store;
   let server = serverForUsers({"foo": "password"}, {
     meta: {global: {engines: {bogus: {version: engine.version, syncID: engine.syncID}}}},
     steam: {}
@@ -541,7 +531,6 @@ add_task(async function test_sql_error() {
   Service.engineManager.register(SteamEngine);
   let engine = Service.engineManager.get("steam");
   engine.enabled = true;
-  let store  = engine._store;
   let server = serverForUsers({"foo": "password"}, {
     meta: {global: {engines: {steam: {version: engine.version,
                                       syncID: engine.syncID}}}},
@@ -569,7 +558,6 @@ add_task(async function test_no_foreign_engines_in_success_ping() {
   Service.engineManager.register(BogusEngine);
   let engine = Service.engineManager.get("bogus");
   engine.enabled = true;
-  let store  = engine._store;
   let server = serverForUsers({"foo": "password"}, {
     meta: {global: {engines: {bogus: {version: engine.version, syncID: engine.syncID}}}},
     steam: {}
diff --git a/services/sync/tps/extensions/tps/resource/modules/bookmarks.jsm b/services/sync/tps/extensions/tps/resource/modules/bookmarks.jsm
index 1a4111b869e5..15e773c3fd85 100644
--- a/services/sync/tps/extensions/tps/resource/modules/bookmarks.jsm
+++ b/services/sync/tps/extensions/tps/resource/modules/bookmarks.jsm
@@ -22,7 +22,7 @@ Cu.import("resource://tps/logger.jsm");
 var DumpBookmarks = function TPS_Bookmarks__DumpBookmarks() {
   let cb = Async.makeSpinningCallback();
   PlacesBackups.getBookmarksTree().then(result => {
-    let [bookmarks, count] = result;
+    let [bookmarks, ] = result;
     Logger.logInfo("Dumping Bookmarks...\n" + JSON.stringify(bookmarks) + "\n\n");
     cb(null);
   }).then(null, error => {
diff --git a/services/sync/tps/extensions/tps/resource/modules/history.jsm b/services/sync/tps/extensions/tps/resource/modules/history.jsm
index c952aa8ee80c..320dc2225b62 100644
--- a/services/sync/tps/extensions/tps/resource/modules/history.jsm
+++ b/services/sync/tps/extensions/tps/resource/modules/history.jsm
@@ -17,13 +17,6 @@ Cu.import("resource://tps/logger.jsm");
 Cu.import("resource://services-common/async.js");
 
 var DumpHistory = function TPS_History__DumpHistory() {
-  let writer = {
-    value: "",
-    write: function PlacesItem__dump__write(aStr, aLen) {
-      this.value += aStr;
-    }
-  };
-
   let query = PlacesUtils.history.getNewQuery();
   let options = PlacesUtils.history.getNewQueryOptions();
   let root = PlacesUtils.history.executeQuery(query, options).root;
diff --git a/services/sync/tps/extensions/tps/resource/modules/tabs.jsm b/services/sync/tps/extensions/tps/resource/modules/tabs.jsm
index 670c0af1e7a1..797a939c09c6 100644
--- a/services/sync/tps/extensions/tps/resource/modules/tabs.jsm
+++ b/services/sync/tps/extensions/tps/resource/modules/tabs.jsm
@@ -49,7 +49,7 @@ var BrowserTabs = {
   Find(uri, title, profile) {
     // Find the uri in Weave's list of tabs for the given profile.
     let engine = Weave.Service.engineManager.get("tabs");
-    for (let [guid, client] of Object.entries(engine.getAllClients())) {
+    for (let [, client] of Object.entries(engine.getAllClients())) {
       if (!client.tabs) {
         continue;
       }
diff --git a/services/sync/tps/extensions/tps/resource/tps.jsm b/services/sync/tps/extensions/tps/resource/tps.jsm
index cdaa0542e104..fd3f3a1ac00c 100644
--- a/services/sync/tps/extensions/tps/resource/tps.jsm
+++ b/services/sync/tps/extensions/tps/resource/tps.jsm
@@ -432,7 +432,6 @@ var TPS = {
     this.shouldValidatePasswords = true;
     try {
       for (let password of passwords) {
-        let password_id = -1;
         Logger.logInfo("executing action " + action.toUpperCase() +
                       " on password " + JSON.stringify(password));
         let passwordOb = new Password(password);