diff --git a/common/bootstrap.js b/common/bootstrap.js
index d131a2b5..de289ee0 100755
--- a/common/bootstrap.js
+++ b/common/bootstrap.js
@@ -37,9 +37,9 @@ function reportError(e) {
     Cc["@mozilla.org/consoleservice;1"].getService(Ci.nsIConsoleService)
                                        .logStringMessage(stack);
 }
-function debug() {
+function debug(...args) {
     if (DEBUG)
-        dump(name + ": " + Array.join(arguments, ", ") + "\n");
+        dump(name + ": " + args.join(", ") + "\n");
 }
 
 function httpGet(uri) {
diff --git a/common/content/commandline.js b/common/content/commandline.js
index 7d0c605b..9ea1fc33 100644
--- a/common/content/commandline.js
+++ b/common/content/commandline.js
@@ -488,9 +488,9 @@ var CommandPromptMode = Class("CommandPromptMode", CommandMode, {
         init.supercall(this);
     },
 
-    complete: function CPM_complete(context) {
+    complete: function CPM_complete(context, ...args) {
         if (this.completer)
-            context.forkapply("prompt", 0, this, "completer", Array.slice(arguments, 1));
+            context.forkapply("prompt", 0, this, "completer", args);
     },
 
     get mode() modes.PROMPT
@@ -955,7 +955,7 @@ var CommandLine = Module("commandline", {
 
     updateOutputHeight: deprecated("mow.resize", function updateOutputHeight(open, extra) mow.resize(open, extra)),
 
-    withOutputToString: function withOutputToString(fn, self) {
+    withOutputToString: function withOutputToString(fn, self, ...args) {
         dactyl.registerObserver("echoLine", observe, true);
         dactyl.registerObserver("echoMultiline", observe, true);
 
@@ -965,7 +965,7 @@ var CommandLine = Module("commandline", {
         }
 
         this.savingOutput = true;
-        dactyl.trapErrors.apply(dactyl, [fn, self].concat(Array.slice(arguments, 2)));
+        dactyl.trapErrors.apply(dactyl, [fn, self].concat(args));
         this.savingOutput = false;
         return output.map(function (elem) elem instanceof Node ? DOM.stringify(elem) : elem)
                      .join("\n");
@@ -1764,8 +1764,7 @@ var CommandLine = Module("commandline", {
                 return Events.PASS;
             });
 
-        let bind = function bind()
-            mappings.add.apply(mappings, [[modes.COMMAND_LINE]].concat(Array.slice(arguments)));
+        let bind = function bind(...args) mappings.add.apply(mappings, [[modes.COMMAND_LINE]].concat(args));
 
         bind(["<Esc>", "<C-[>"], "Stop waiting for completions or exit Command Line mode",
              function ({ self }) {
diff --git a/common/content/dactyl.js b/common/content/dactyl.js
index a0bcda8e..b197abbc 100644
--- a/common/content/dactyl.js
+++ b/common/content/dactyl.js
@@ -235,8 +235,8 @@ var Dactyl = Module("dactyl", XPCOM(Ci.nsISupportsWeakReference, ModuleBase), {
             });
     },
 
-    triggerObserver: function triggerObserver(type) {
-        return this.applyTriggerObserver(type, Array.slice(arguments, 1));
+    triggerObserver: function triggerObserver(type, ...args) {
+        return this.applyTriggerObserver(type, args);
     },
 
     addUsageCommand: function (params) {
@@ -523,10 +523,10 @@ var Dactyl = Module("dactyl", XPCOM(Ci.nsISupportsWeakReference, ModuleBase), {
      * Acts like the Function builtin, but the code executes in the
      * userContext global.
      */
-    userFunc: function userFunc() {
+    userFunc: function userFunc(...args) {
         return this.userEval(
-            "(function userFunction(" + Array.slice(arguments, 0, -1).join(", ") + ")" +
-            " { " + arguments[arguments.length - 1] + " })");
+            "(function userFunction(" + args.slice(0, -1).join(", ") + ")" +
+            " { " + args.pop() + " })");
     },
 
     /**
@@ -1116,11 +1116,11 @@ var Dactyl = Module("dactyl", XPCOM(Ci.nsISupportsWeakReference, ModuleBase), {
      * @param {function} func The function to call
      * @param {object} self The 'this' object for the function.
      */
-    trapErrors: function trapErrors(func, self) {
+    trapErrors: function trapErrors(func, self, ...args) {
         try {
             if (isString(func))
                 func = self[func];
-            return func.apply(self || this, Array.slice(arguments, 2));
+            return func.apply(self || this, args);
         }
         catch (e) {
             try {
diff --git a/common/content/editor.js b/common/content/editor.js
index 89914d27..25dff89b 100644
--- a/common/content/editor.js
+++ b/common/content/editor.js
@@ -1324,8 +1324,7 @@ var Editor = Module("editor", XPCOM(Ci.nsIEditActionListener, ModuleBase), {
             },
             { count: true });
 
-        let bind = function bind() mappings.add.apply(mappings,
-                                                      [[modes.AUTOCOMPLETE]].concat(Array.slice(arguments)));
+        let bind = function bind(...args) mappings.add.apply(mappings, [[modes.AUTOCOMPLETE]].concat(args));
 
         bind(["<Esc>"], "Return to Insert mode",
              function () Events.PASS_THROUGH);
diff --git a/common/content/history.js b/common/content/history.js
index 9f2a2d95..f19b1e24 100644
--- a/common/content/history.js
+++ b/common/content/history.js
@@ -352,7 +352,7 @@ var History = Module("history", {
         completion.addUrlCompleter("history", "History", completion.history);
     },
     mappings: function initMappings() {
-        function bind() mappings.add.apply(mappings, [config.browserModes].concat(Array.slice(arguments)));
+        function bind(...args) mappings.add.apply(mappings, [config.browserModes].concat(args));
 
         bind(["<C-o>"], "Go to an older position in the jump list",
              function ({ count }) { history.stepTo(-Math.max(count, 1), true); },
diff --git a/common/modules/addons.jsm b/common/modules/addons.jsm
index bfe53a66..e2c577ad 100644
--- a/common/modules/addons.jsm
+++ b/common/modules/addons.jsm
@@ -15,8 +15,7 @@ defineModule("addons", {
 this.lazyRequire("completion", ["completion"]);
 lazyRequire("template", ["template"]);
 
-var callResult = function callResult(method) {
-    let args = Array.slice(arguments, 1);
+var callResult = function callResult(method, ...args) {
     return function (result) { result[method].apply(result, args); };
 }
 
diff --git a/common/modules/base.jsm b/common/modules/base.jsm
index cdeb598a..a9318eb4 100644
--- a/common/modules/base.jsm
+++ b/common/modules/base.jsm
@@ -68,8 +68,8 @@ Object.defineProperty(defineModule.loadLog, "push", {
     }
 });
 defineModule.prefix = "";
-defineModule.dump = function dump_() {
-    let msg = Array.map(arguments, function (msg) {
+defineModule.dump = function dump_(...args) {
+    let msg = args.map(function (msg) {
         if (loaded.util && typeof msg == "object")
             msg = util.objectToString(msg);
         return msg;
@@ -78,13 +78,13 @@ defineModule.dump = function dump_() {
                .replace(/^./gm, JSMLoader.name + ": $&"));
 }
 defineModule.modules = [];
-defineModule.time = function time(major, minor, func, self) {
+defineModule.time = function time(major, minor, func, self, ...args) {
     let time = Date.now();
     if (typeof func !== "function")
         func = self[func];
 
     try {
-        var res = func.apply(self, Array.slice(arguments, 4));
+        var res = func.apply(self, args);
     }
     catch (e) {
         loaded.util && util.reportError(e);
@@ -441,18 +441,18 @@ function curry(fn, length, self, acc) {
         return fn;
 
     // Close over function with 'this'
-    function close(self, fn) function () fn.apply(self, Array.slice(arguments));
+    function close(self, fn) function () fn.apply(self, arguments);
 
     if (acc == null)
         acc = [];
 
-    return function curried() {
-        let args = acc.concat(Array.slice(arguments));
-
+    return function curried(...args) {
         // The curried result should preserve 'this'
-        if (arguments.length == 0)
+        if (args.length == 0)
             return close(self || this, curried);
 
+        let args = acc.concat(args);
+
         if (args.length >= length)
             return fn.apply(self || this, args);
 
@@ -461,15 +461,14 @@ function curry(fn, length, self, acc) {
 }
 
 if (curry.bind)
-    var bind = function bind(meth, self) let (func = callable(meth) ? meth : self[meth])
-        func.bind.apply(func, Array.slice(arguments, 1));
+    var bind = function bind(meth, self, ...args) let (func = callable(meth) ? meth : self[meth])
+        func.bind.apply(func, [self].concat(args));
 else
-    var bind = function bind(func, self) {
+    var bind = function bind(func, self, ...args) {
         if (!callable(func))
             func = self[func];
 
-        let args = Array.slice(arguments, bind.length);
-        return function bound() func.apply(self, args.concat(Array.slice(arguments)));
+        return function bound(...args2) func.apply(self, args.concat(args2));
     };
 
 /**
@@ -574,8 +573,8 @@ function isString(val) objproto.toString.call(val) == "[object String]";
  */
 function callable(val) typeof val === "function" && !(val instanceof Ci.nsIDOMElement);
 
-function call(fn) {
-    fn.apply(arguments[1], Array.slice(arguments, 2));
+function call(fn, self, ...args) {
+    fn.apply(self, args);
     return fn;
 }
 
@@ -660,8 +659,8 @@ function update(target) {
                         func.superapply = function superapply(self, args)
                             let (meth = Object.getPrototypeOf(target)[k])
                                 meth && meth.apply(self, args);
-                        func.supercall = function supercall(self)
-                            func.superapply(self, Array.slice(arguments, 1));
+                        func.supercall = function supercall(self, ...args)
+                            func.superapply(self, args);
                     }
                 }
                 Object.defineProperty(target, k, desc);
@@ -687,8 +686,8 @@ function update_(target) {
                         func.superapply = function super_apply(self, args)
                             let (meth = Object.getPrototypeOf(target)[k])
                                 meth && meth.apply(self, args);
-                        func.supercall = function super_call(self)
-                            func.superapply(self, Array.slice(arguments, 1));
+                        func.supercall = function super_call(self, ...args)
+                            func.superapply(self, args);
                     }
                 }
                 Object.defineProperty(target, k, desc);
@@ -722,9 +721,8 @@ function update_(target) {
  *
  * @returns {function} The constructor for the resulting class.
  */
-function Class() {
+function Class(...args) {
 
-    var args = Array.slice(arguments);
     if (isString(args[0]))
         var name = args.shift();
     var superclass = Class;
@@ -991,8 +989,8 @@ Class.prototype = {
                             return meth && meth.apply(self, args);
                         };
 
-                        func.supercall = function supercall(self) {
-                            return func.superapply(self, Array.slice(arguments, 1));
+                        func.supercall = function supercall(self, ...args) {
+                            return func.superapply(self, args);
                         }
                     }
                 }
@@ -1129,22 +1127,22 @@ var Finished = Class("Finished", ErrorBase);
  * @param {Object} classProperties Properties to be applied to the class constructor.
  * @returns {Class}
  */
-function Module(name, prototype) {
+function Module(name, prototype, ...args) {
     try {
-        let init = callable(prototype) ? 4 : 3;
-        let proto = arguments[callable(prototype) ? 2 : 1];
+        let init = callable(prototype) ? 2 : 1;
+        let proto = callable(prototype) ? args[0] : prototype;
 
         proto._metaInit_ = function () {
             delete module.prototype._metaInit_;
             currentModule[name.toLowerCase()] = this;
         };
 
-        const module = Class.apply(Class, Array.slice(arguments, 0, init));
+        const module = Class.apply(Class, [name, prototype, ...args.slice(0, init)]);
         let instance = module();
         module.className = name.toLowerCase();
 
         instance.INIT = update(Object.create(Module.INIT),
-                               arguments[init] || {});
+                               args[init] || {});
 
         currentModule[module.className] = instance;
         defineModule.modules.push(instance);
@@ -1201,13 +1199,9 @@ Module.INIT = {
  *
  * @returns {function} The constructor for the new Struct.
  */
-function Struct() {
-    if (!/^[A-Z]/.test(arguments[0]))
-        var args = Array.slice(arguments, 0);
-    else {
-        var className = arguments[0];
-        args = Array.slice(arguments, 1);
-    }
+function Struct(...args) {
+    if (/^[A-Z]/.test(args[0]))
+        var className = args.shift();
 
     const Struct = Class(className || "Struct", StructBase, {
         length: args.length,
@@ -1601,9 +1595,9 @@ var array = Class("array", Array, {
             },
             array: ary,
             toString: function () this.array.toString(),
-            concat: function () this.__noSuchMethod__("concat", Array.slice(arguments)),
-            filter: function () this.__noSuchMethod__("filter", Array.slice(arguments)),
-            map: function () this.__noSuchMethod__("map", Array.slice(arguments))
+            concat: function (...args) this.__noSuchMethod__("concat", args),
+            filter: function (...args) this.__noSuchMethod__("filter", args),
+            map: function (...args) this.__noSuchMethod__("map", args)
         };
     }
 }, {
@@ -1736,8 +1730,8 @@ var array = Class("array", Array, {
 /* Make Minefield not explode, because Minefield exploding is not fun. */
 let iterProto = Iter.prototype;
 Object.keys(iter).forEach(function (k) {
-    iterProto[k] = function () {
-        let res = iter[k].apply(iter, [this].concat(Array.slice(arguments)));
+    iterProto[k] = function (...args) {
+        let res = iter[k].apply(iter, [this].concat(args));
         if (isinstance(res, ["Iterator", "Generator"]))
             return Iter(res);
         return res;
@@ -1746,8 +1740,8 @@ Object.keys(iter).forEach(function (k) {
 
 Object.keys(array).forEach(function (k) {
     if (!(k in iterProto))
-        iterProto[k] = function () {
-            let res = array[k].apply(array, [this.toArray()].concat(Array.slice(arguments)));
+        iterProto[k] = function (...args) {
+            let res = array[k].apply(array, [this.toArray()].concat(args));
             if (isinstance(res, ["Iterator", "Generator"]))
                 return Iter(res);
             if (isArray(res))
diff --git a/common/modules/commands.jsm b/common/modules/commands.jsm
index f083ff7c..617c6bd1 100644
--- a/common/modules/commands.jsm
+++ b/common/modules/commands.jsm
@@ -1571,7 +1571,7 @@ var Commands = Module("commands", {
                                     return dactyl.userEval(completer);
                                 });
                                 if (callable(result))
-                                    return result.apply(this, Array.slice(arguments));
+                                    return result.apply(this, arguments);
                                 else
                                     return context.completions = result;
                             };
diff --git a/common/modules/completion.jsm b/common/modules/completion.jsm
index d3967880..09491706 100644
--- a/common/modules/completion.jsm
+++ b/common/modules/completion.jsm
@@ -705,8 +705,8 @@ var CompletionContext = Class("CompletionContext", {
      *      for the new context. If a string is provided, it is
      *      interpreted as a method to access on *self*.
      */
-    fork: function fork(name, offset, self, completer) {
-        return this.forkapply(name, offset, self, completer, Array.slice(arguments, fork.length));
+    fork: function fork(name, offset, self, completer, ...args) {
+        return this.forkapply(name, offset, self, completer, args);
     },
 
     forkapply: function forkapply(name, offset, self, completer, args) {
@@ -731,7 +731,7 @@ var CompletionContext = Class("CompletionContext", {
         return context;
     },
 
-    split: function split(name, obj, fn) {
+    split: function split(name, obj, fn, ...args) {
         let context = this.fork(name);
         let alias = (prop) => {
             context.__defineGetter__(prop, () => this[prop]);
@@ -746,7 +746,7 @@ var CompletionContext = Class("CompletionContext", {
         context.hasItems = true;
         this.hasItems = false;
         if (fn)
-            return fn.apply(obj || this, [context].concat(Array.slice(arguments, split.length)));
+            return fn.apply(obj || this, [context].concat(args));
         return context;
     },
 
@@ -903,10 +903,10 @@ var Completion = Module("completion", {
         get options() modules.options,
 
         // FIXME
-        _runCompleter: function _runCompleter(name, filter, maxItems) {
+        _runCompleter: function _runCompleter(name, filter, maxItems, ...args) {
             let context = modules.CompletionContext(filter);
             context.maxItems = maxItems;
-            let res = context.fork.apply(context, ["run", 0, this, name].concat(Array.slice(arguments, 3)));
+            let res = context.fork.apply(context, ["run", 0, this, name].concat(args));
             if (res) {
                 if (Components.stack.caller.name === "runCompleter") // FIXME
                     return { items: res.map(function m(i) ({ item: i })) };
@@ -917,14 +917,14 @@ var Completion = Module("completion", {
         },
 
         runCompleter: function runCompleter(name, filter, maxItems) {
-            return this._runCompleter.apply(this, Array.slice(arguments))
+            return this._runCompleter.apply(this, arguments)
                        .items.map(function m(i) i.item);
         },
 
-        listCompleter: function listCompleter(name, filter, maxItems) {
+        listCompleter: function listCompleter(name, filter, maxItems, ...args) {
             let context = modules.CompletionContext(filter || "");
             context.maxItems = maxItems;
-            context.fork.apply(context, ["list", 0, this, name].concat(Array.slice(arguments, 3)));
+            context.fork.apply(context, ["list", 0, this, name].concat(args));
             context = context.contexts["/list"];
             context.wait(null, true);
 
@@ -987,9 +987,9 @@ var Completion = Module("completion", {
         }, this);
     },
 
-    addUrlCompleter: function addUrlCompleter(opt) {
-        let completer = Completion.UrlCompleter.apply(null, Array.slice(arguments));
-        completer.args = Array.slice(arguments, completer.length);
+    addUrlCompleter: function addUrlCompleter(opt, ...args) {
+        let completer = Completion.UrlCompleter.apply(null, [opt, ...args]);
+        completer.args = args;
         this.urlCompleters[opt] = completer;
     },
 
diff --git a/common/modules/contexts.jsm b/common/modules/contexts.jsm
index b75d32c4..ffada2b7 100644
--- a/common/modules/contexts.jsm
+++ b/common/modules/contexts.jsm
@@ -65,7 +65,7 @@ var Group = Class("Group", {
     get builtin() this.modules.contexts.builtinGroups.indexOf(this) >= 0,
 
 }, {
-    compileFilter: function (patterns, default_) {
+    compileFilter: function (patterns, default_ = false) {
         if (arguments.length < 2)
             default_ = false;
 
diff --git a/common/modules/javascript.jsm b/common/modules/javascript.jsm
index 06e4aa55..b74c86f4 100644
--- a/common/modules/javascript.jsm
+++ b/common/modules/javascript.jsm
@@ -855,8 +855,7 @@ var JavaScript = Module("javascript", {
     mappings: function initMappings(dactyl, modules, window) {
         const { mappings, modes } = modules;
 
-        function bind() mappings.add.apply(mappings,
-                                           [[modes.REPL]].concat(Array.slice(arguments)))
+        function bind(...args) mappings.add.apply(mappings, [[modes.REPL]].concat(args))
 
         bind(["<Return>"], "Accept the current input",
              function ({ self }) { self.accept(); });
diff --git a/common/modules/main.jsm b/common/modules/main.jsm
index 555d2947..ae6926d0 100644
--- a/common/modules/main.jsm
+++ b/common/modules/main.jsm
@@ -65,14 +65,13 @@ var Modules = function Modules(window) {
      *
      * @returns {function} The constructor for the resulting module.
      */
-    function Module(name) {
-        let args = Array.slice(arguments);
+    function Module(name, ...args) {
 
         var base = ModuleBase;
-        if (callable(args[1]))
-            base = args.splice(1, 1)[0];
+        if (callable(args[0]))
+            base = args.shift();
 
-        let [, prototype, classProperties, moduleInit] = args;
+        let [prototype, classProperties, moduleInit] = args;
         prototype._metaInit_ = function () {
             delete module.prototype._metaInit_;
             Class.replaceProperty(modules, module.className, this);
diff --git a/common/modules/messages.jsm b/common/modules/messages.jsm
index 238be527..533c0043 100644
--- a/common/modules/messages.jsm
+++ b/common/modules/messages.jsm
@@ -98,7 +98,7 @@ var Messages = Module("messages", {
         file = io.File(file);
 
         function properties(base, iter_, prop) iter(function _properties() {
-            function key() [base, obj.identifier || obj.name].concat(Array.slice(arguments)).join(".").replace(/[\\:=]/g, "\\$&");
+            function key(...args) [base, obj.identifier || obj.name].concat(args).join(".").replace(/[\\:=]/g, "\\$&");
 
             prop = prop || "description";
             for (var obj in iter_) {
diff --git a/common/modules/util.jsm b/common/modules/util.jsm
index 436db405..bf7b67ee 100644
--- a/common/modules/util.jsm
+++ b/common/modules/util.jsm
@@ -1622,11 +1622,11 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
      * @param {function} func The function to call
      * @param {object} self The 'this' object for the function.
      */
-    trapErrors: function trapErrors(func, self) {
+    trapErrors: function trapErrors(func, self, ...args) {
         try {
             if (!callable(func))
                 func = self[func];
-            return func.apply(self || this, Array.slice(arguments, 2));
+            return func.apply(self || this, args);
         }
         catch (e) {
             this.reportError(e);
@@ -1708,9 +1708,9 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
      * @param {object} self The 'this' object of the method.
      * @param ... Arguments to pass to *meth*.
      */
-    withProperErrors: function withProperErrors(meth, self) {
+    withProperErrors: function withProperErrors(meth, self, ...args) {
         try {
-            return (callable(meth) ? meth : self[meth]).apply(self, Array.slice(arguments, withProperErrors.length));
+            return (callable(meth) ? meth : self[meth]).apply(self, args);
         }
         catch (e) {
             throw e.stack ? e : Error(e);
diff --git a/common/tests/functional/dactyl.jsm b/common/tests/functional/dactyl.jsm
index a9555e21..d738da63 100644
--- a/common/tests/functional/dactyl.jsm
+++ b/common/tests/functional/dactyl.jsm
@@ -389,10 +389,10 @@ Controller.prototype = {
      * @param {...} Extra arguments are passed to the completion
      *     function directly.
      */
-    testCompleter: wrapAssertNoErrors(function testCompleter(self, func, string, message) {
+    testCompleter: wrapAssertNoErrors(function testCompleter(self, func, string, message, ...args) {
         var context = this.modules.CompletionContext(string || "");
         context.tabPressed = true;
-        context.forkapply("completions", 0, self, func, Array.slice(arguments, testCompleter.length));
+        context.forkapply("completions", 0, self, func, args);
 
         utils.assert("dactyl.runCompletions", context.wait(5000),
                      message || "Completion failed: " + self + "." + func);
diff --git a/common/tests/functional/testCommands.js b/common/tests/functional/testCommands.js
index 2f986259..3382cd98 100644
--- a/common/tests/functional/testCommands.js
+++ b/common/tests/functional/testCommands.js
@@ -985,9 +985,9 @@ function _runCommands(cmdName, testName, commands) {
     });
 }
 
-function runTest(message, test) {
+function runTest(message, test, ...args) {
     if (test)
-        var res = test.apply(null, Array.slice(arguments, runTest.length));
+        var res = test.apply(null, args);
     if (res !== undefined)
         jumlib.assert(res, message);
 }