diff --git a/caps/tests/mochitest/test_addonMayLoad.html b/caps/tests/mochitest/test_addonMayLoad.html
index 2d5e5e59f155..74dc8134b485 100644
--- a/caps/tests/mochitest/test_addonMayLoad.html
+++ b/caps/tests/mochitest/test_addonMayLoad.html
@@ -23,7 +23,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1180921
       baseURL: `file:///{id}`,
 
       allowedOrigins: new MatchPatternSet([`*://${subdomain}.example.org/*`]),
-      localizeCallback(string) {},
+      localizeCallback() {},
     });
   }
 
diff --git a/caps/tests/mochitest/test_bug995943.xhtml b/caps/tests/mochitest/test_bug995943.xhtml
index 0ba95f548d52..fc7c0b022fac 100644
--- a/caps/tests/mochitest/test_bug995943.xhtml
+++ b/caps/tests/mochitest/test_bug995943.xhtml
@@ -33,7 +33,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=995943
 
   function checkLoadFileURI(domain, shouldLoad) {
     debug("Invoking checkLoadFileURI with domain: " + domain + ", shouldLoad: " + shouldLoad);
-    return new Promise(function(resolve, reject) {
+    return new Promise(function(resolve) {
       $('ifr').addEventListener('load', function l1() {
         debug("Invoked l1 for " + domain);
         $('ifr').removeEventListener('load', l1);
diff --git a/chrome/test/unit/test_bug564667.js b/chrome/test/unit/test_bug564667.js
index 7ee5229827df..31fbb1b8c248 100644
--- a/chrome/test/unit/test_bug564667.js
+++ b/chrome/test/unit/test_bug564667.js
@@ -27,7 +27,7 @@ function test_mapping(chromeURL, target) {
 /*
  * Checks that a mapping was removed
  */
-function test_removed_mapping(chromeURL, target) {
+function test_removed_mapping(chromeURL) {
   var uri = Services.io.newURI(chromeURL);
   try {
     gCR.convertChromeURL(uri);
diff --git a/intl/locale/tests/unit/data/intl_on_workers_worker.js b/intl/locale/tests/unit/data/intl_on_workers_worker.js
index e6f01e71a826..9b47fdf18124 100644
--- a/intl/locale/tests/unit/data/intl_on_workers_worker.js
+++ b/intl/locale/tests/unit/data/intl_on_workers_worker.js
@@ -1,6 +1,6 @@
 /* eslint-env worker */
 
-self.onmessage = function (data) {
+self.onmessage = function () {
   let myLocale = Intl.NumberFormat().resolvedOptions().locale;
   self.postMessage(myLocale);
 };
diff --git a/intl/locale/tests/unit/test_localeService.js b/intl/locale/tests/unit/test_localeService.js
index ae2d949e806e..7d55b7fc251a 100644
--- a/intl/locale/tests/unit/test_localeService.js
+++ b/intl/locale/tests/unit/test_localeService.js
@@ -69,7 +69,7 @@ add_test(function test_requestedLocales_matchOS() {
   Services.prefs.setCharPref(PREF_REQUESTED_LOCALES, "ar-IR");
 
   const observer = {
-    observe(aSubject, aTopic, aData) {
+    observe(aSubject, aTopic) {
       switch (aTopic) {
         case REQ_LOC_CHANGE_EVENT:
           const reqLocs = localeService.requestedLocales;
@@ -97,7 +97,7 @@ add_test(function test_requestedLocales_onChange() {
   Services.prefs.setCharPref(PREF_REQUESTED_LOCALES, "ar-IR");
 
   const observer = {
-    observe(aSubject, aTopic, aData) {
+    observe(aSubject, aTopic) {
       switch (aTopic) {
         case REQ_LOC_CHANGE_EVENT:
           const reqLocs = localeService.requestedLocales;
diff --git a/intl/uconv/tests/unit/test_charset_conversion.js b/intl/uconv/tests/unit/test_charset_conversion.js
index 577a80108177..edbc83b83c70 100644
--- a/intl/uconv/tests/unit/test_charset_conversion.js
+++ b/intl/uconv/tests/unit/test_charset_conversion.js
@@ -138,7 +138,7 @@ function getUnicharInputStream(filename, encoding) {
   return new CIS(fis, encoding, 8192, 0x0);
 }
 
-function getBinaryInputStream(filename, encoding) {
+function getBinaryInputStream(filename) {
   var file = dataDir.clone();
   file.append(filename);
 
diff --git a/taskcluster/docker/periodic-updates/scripts/getHSTSPreloadList.js b/taskcluster/docker/periodic-updates/scripts/getHSTSPreloadList.js
index aeaa29bc2dc3..b695f0dd9077 100644
--- a/taskcluster/docker/periodic-updates/scripts/getHSTSPreloadList.js
+++ b/taskcluster/docker/periodic-updates/scripts/getHSTSPreloadList.js
@@ -160,16 +160,16 @@ function RedirectAndAuthStopper() {}
 
 RedirectAndAuthStopper.prototype = {
   // nsIChannelEventSink
-  asyncOnChannelRedirect(oldChannel, newChannel, flags, callback) {
+  asyncOnChannelRedirect() {
     throw Components.Exception("", Cr.NS_ERROR_ENTITY_CHANGED);
   },
 
   // nsIAuthPrompt2
-  promptAuth(channel, level, authInfo) {
+  promptAuth() {
     return false;
   },
 
-  asyncPromptAuth(channel, callback, context, level, authInfo) {
+  asyncPromptAuth() {
     throw Components.Exception("", Cr.NS_ERROR_NOT_IMPLEMENTED);
   },
 
@@ -184,7 +184,7 @@ RedirectAndAuthStopper.prototype = {
 };
 
 function fetchstatus(host) {
-  return new Promise((resolve, reject) => {
+  return new Promise(resolve => {
     let xhr = new XMLHttpRequest();
     let uri = "https://" + host.name + "/";
 
diff --git a/tools/esmify/use-import-export-declarations.js b/tools/esmify/use-import-export-declarations.js
index fe8c4dd286af..60e017645bbc 100644
--- a/tools/esmify/use-import-export-declarations.js
+++ b/tools/esmify/use-import-export-declarations.js
@@ -111,7 +111,7 @@ function isTopLevel(path) {
   return path.parent.node.type === "Program";
 }
 
-function convertToExport(jscodeshift, path, name) {
+function convertToExport(jscodeshift, path) {
   const e = jscodeshift.exportNamedDeclaration(path.node);
   e.comments = [];
   e.comments = path.node.comments;
diff --git a/tools/tryselect/selectors/chooser/static/filter.js b/tools/tryselect/selectors/chooser/static/filter.js
index 2d8731e61fde..683ced8953b7 100644
--- a/tools/tryselect/selectors/chooser/static/filter.js
+++ b/tools/tryselect/selectors/chooser/static/filter.js
@@ -10,7 +10,7 @@ const pluralize = (count, noun, suffix = "s") =>
 var selected = [];
 
 var updateLabels = () => {
-  $(".tab-pane.active > .filter-label").each(function (index) {
+  $(".tab-pane.active > .filter-label").each(function () {
     let box = $("#" + this.htmlFor)[0];
     let method = box.checked ? "add" : "remove";
     $(this)[method + "Class"]("is-checked");
@@ -21,7 +21,7 @@ var apply = () => {
   let filters = {};
   let kinds = [];
 
-  $(".filter:checked").each(function (index) {
+  $(".filter:checked").each(function () {
     for (let kind of this.name.split(",")) {
       if (!kinds.includes(kind)) {
         kinds.push(kind);
@@ -76,7 +76,7 @@ var apply = () => {
 var applyChunks = () => {
   // For tasks that have a chunk filter applied, we handle that here.
   let filters = {};
-  $(".filter:text").each(function (index) {
+  $(".filter:text").each(function () {
     let value = $(this).val();
     if (value === "") {
       return;
diff --git a/tools/tryselect/selectors/chooser/static/select.js b/tools/tryselect/selectors/chooser/static/select.js
index 8a315c0a52cf..e90744a09add 100644
--- a/tools/tryselect/selectors/chooser/static/select.js
+++ b/tools/tryselect/selectors/chooser/static/select.js
@@ -39,7 +39,7 @@ labels.click(function (e) {
 
 function selectAll(btn) {
   let checked = !!btn.value;
-  $("div.active label.filter-label").each(function (index) {
+  $("div.active label.filter-label").each(function () {
     $(this).find("input:checkbox")[0].checked = checked;
   });
   apply();
diff --git a/xpcom/tests/unit/test_bug325418.js b/xpcom/tests/unit/test_bug325418.js
index 5840aacf740a..c86f8d584518 100644
--- a/xpcom/tests/unit/test_bug325418.js
+++ b/xpcom/tests/unit/test_bug325418.js
@@ -8,7 +8,7 @@ var gStartTime2;
 var timer;
 
 var observer1 = {
-  observe: function observeTC1(subject, topic, data) {
+  observe: function observeTC1(subject, topic) {
     if (topic == "timer-callback") {
       // Stop timer, so it doesn't repeat (if test runs slowly).
       timer.cancel();
@@ -30,7 +30,7 @@ var observer1 = {
 };
 
 var observer2 = {
-  observe: function observeTC2(subject, topic, data) {
+  observe: function observeTC2(subject, topic) {
     if (topic == "timer-callback") {
       // Stop timer, so it doesn't repeat (if test runs slowly).
       timer.cancel();
diff --git a/xpcom/tests/unit/test_nsIProcess.js b/xpcom/tests/unit/test_nsIProcess.js
index 582d10440c3e..e8a382b29fe1 100644
--- a/xpcom/tests/unit/test_nsIProcess.js
+++ b/xpcom/tests/unit/test_nsIProcess.js
@@ -128,7 +128,7 @@ function test_notify_blocking() {
   process.init(file);
 
   process.runAsync([], 0, {
-    observe(subject, topic, data) {
+    observe(subject, topic) {
       process = subject.QueryInterface(Ci.nsIProcess);
       Assert.equal(topic, "process-failed");
       Assert.equal(process.exitValue, 42);
@@ -145,7 +145,7 @@ function test_notify_nonblocking() {
   process.init(file);
 
   process.runAsync(TEST_ARGS, TEST_ARGS.length, {
-    observe(subject, topic, data) {
+    observe(subject, topic) {
       process = subject.QueryInterface(Ci.nsIProcess);
       Assert.equal(topic, "process-finished");
       Assert.equal(process.exitValue, 0);
@@ -162,7 +162,7 @@ function test_notify_killed() {
   process.init(file);
 
   process.runAsync([], 0, {
-    observe(subject, topic, data) {
+    observe(subject, topic) {
       process = subject.QueryInterface(Ci.nsIProcess);
       Assert.equal(topic, "process-failed");
       do_test_finished();
diff --git a/xpcom/tests/unit/test_windows_registry.js b/xpcom/tests/unit/test_windows_registry.js
index 691c0461c3fa..ef5082a6663e 100644
--- a/xpcom/tests/unit/test_windows_registry.js
+++ b/xpcom/tests/unit/test_windows_registry.js
@@ -172,7 +172,7 @@ function test_childkey_functions(testKey) {
   strictEqual(testKey.hasChild(TESTDATA_CHILD_KEY), false);
 }
 
-function cleanup_test_run(testKey, keyName) {
+function cleanup_test_run(testKey) {
   info("Cleaning up test.");
 
   for (var i = 0; i < testKey.childCount; i++) {