diff --git a/common/locale/en-US/options.xml b/common/locale/en-US/options.xml
index 189e283c..73217611 100644
--- a/common/locale/en-US/options.xml
+++ b/common/locale/en-US/options.xml
@@ -77,6 +77,13 @@
     the form of <tt>&lt;e-<a>name</a>></tt>, its value is never shown but may be
     used to test whether the given parameter is empty.
 </p>
+<p>
+    Array elements, such as in the the <tt>&lt;args></tt> parameter
+    of <ex>:command</ex> macros, may be accessed by appending
+    <tt>[<a>n</a>]</tt>, where <a>n</a> is the one-based array
+    index, to the macro name. The first argument of a command is
+    therefore accessed with <tt>&lt;args[1]&lt;</tt>.
+</p>
 <p>
     Any substring enclosed by <em><tt>&lt;{</tt></em> and <em><tt>}></tt></em>
     is automatically elided if any of the contained macros aren't currently
diff --git a/common/modules/base.jsm b/common/modules/base.jsm
index 8b451b24..ded0ab18 100644
--- a/common/modules/base.jsm
+++ b/common/modules/base.jsm
@@ -716,18 +716,28 @@ function Class() {
     if (callable(args[0]))
         superclass = args.shift();
 
-    var Constructor = eval(String.replace(<![CDATA[
-        (function constructor(PARAMS) {
+    if (loaded.util && util.haveGecko("6.0a1")) // Bug 657418.
+        var Constructor = function Constructor() {
             var self = Object.create(Constructor.prototype, {
                 constructor: { value: Constructor },
             });
             self.instance = self;
             var res = self.init.apply(self, arguments);
             return res !== undefined ? res : self;
-        })]]>,
-        "constructor", (name || superclass.className).replace(/\W/g, "_"))
-            .replace("PARAMS", /^function .*?\((.*?)\)/.exec(args[0] && args[0].init || Class.prototype.init)[1]
-                                                       .replace(/\b(self|res|Constructor)\b/g, "$1_")));
+        };
+    else
+        var Constructor = eval(String.replace(<![CDATA[
+            (function constructor(PARAMS) {
+                var self = Object.create(Constructor.prototype, {
+                    constructor: { value: Constructor },
+                });
+                self.instance = self;
+                var res = self.init.apply(self, arguments);
+                return res !== undefined ? res : self;
+            })]]>,
+            "constructor", (name || superclass.className).replace(/\W/g, "_"))
+                .replace("PARAMS", /^function .*?\((.*?)\)/.exec(args[0] && args[0].init || Class.prototype.init)[1]
+                                                           .replace(/\b(self|res|Constructor)\b/g, "$1_")));
 
     Constructor.className = name || superclass.className || superclass.name;
 
diff --git a/common/modules/util.jsm b/common/modules/util.jsm
index 6d6868e8..f5ce09d0 100644
--- a/common/modules/util.jsm
+++ b/common/modules/util.jsm
@@ -356,14 +356,14 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
             ([^]*?) // 1
             (?:
                 (<\{) | // 2
-                (< ((?:[a-z]-)?[a-z-]+?) >) | // 3 4
-                (\}>) // 5
+                (< ((?:[a-z]-)?[a-z-]+?) (?:\[([0-9]+)\])? >) | // 3 4 5
+                (\}>) // 6
             )
         ]]>, "gixy");
         macro = String(macro);
         let end = 0;
         for (let match in re.iterate(macro)) {
-            let [, prefix, open, full, macro, close] = match;
+            let [, prefix, open, full, macro, idx, close] = match;
             end += match[0].length;
 
             if (prefix)
@@ -390,9 +390,17 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
                 if (set.has(defaults, name))
                     stack.top.elements.push(quote(defaults[name]));
                 else {
-                    stack.top.elements.push(update(
-                        function (obj) obj[name] != null ? quote(obj[name]) : set.has(obj, name) ? "" : unknown(full),
-                        { test: function (obj) obj[name] != null && obj[name] !== false && (!flags.e || obj[name] != "") }));
+                    if (idx) {
+                        idx = Number(idx) - 1;
+                        stack.top.elements.push(update(
+                            function (obj) obj[name] != null && idx in obj[name] ? quote(obj[name][idx]) : set.has(obj, name) ? "" : unknown(full),
+                            { test: function (obj) obj[name] != null && idx in obj[name] && obj[name][idx] !== false && (!flags.e || obj[name][idx] != "") }));
+                    }
+                    else {
+                        stack.top.elements.push(update(
+                            function (obj) obj[name] != null ? quote(obj[name]) : set.has(obj, name) ? "" : unknown(full),
+                            { test: function (obj) obj[name] != null && obj[name] !== false && (!flags.e || obj[name] != "") }));
+                    }
 
                     for (let elem in array.iterValues(stack))
                         elem.seen[name] = true;
@@ -1252,7 +1260,7 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
                 delete desc.writable;
                 desc.get = function get() value;
                 desc.set = function set(val) {
-                    if (String(val).indexOf(sentinel) < 0)
+                    if (!callable(val) || Function.prototype.toString(val).indexOf(sentinel) < 0)
                         Class.replaceProperty(this, k, val);
                     else {
                         let package_ = util.newURI(util.fixURI(Components.stack.caller.filename)).host;
diff --git a/pentadactyl/install.rdf b/pentadactyl/install.rdf
index 341c0e6d..71433f61 100644
--- a/pentadactyl/install.rdf
+++ b/pentadactyl/install.rdf
@@ -32,7 +32,7 @@
             <Description
                 em:id="{ec8030f7-c20a-464f-9b0e-13a3a9e97384}"
                 em:minVersion="3.6"
-                em:maxVersion="6.*"/>
+                em:maxVersion="7.*"/>
         </em:targetApplication>
     </Description>
 </RDF>