diff --git a/common/content/abbreviations.js b/common/content/abbreviations.js
index 1c81b1d5..4338da88 100644
--- a/common/content/abbreviations.js
+++ b/common/content/abbreviations.js
@@ -267,7 +267,7 @@ var Abbreviations = Module("abbreviations", {
         let hives = (hives || this.userHives).filter(h => !h.empty);
 
         function abbrevs(hive)
-            hive.merged.filter(ab => (ab.inModes(modes) && ab.lhs.indexOf(lhs) == 0));
+            hive.merged.filter(ab => (ab.inModes(modes) && ab.lhs.startsWith(lhs)));
 
         let list = ["table", {},
                 ["tr", { highlight: "Title" },
diff --git a/common/content/bookmarks.js b/common/content/bookmarks.js
index 842fc894..3e3c254e 100644
--- a/common/content/bookmarks.js
+++ b/common/content/bookmarks.js
@@ -656,7 +656,7 @@ var Bookmarks = Module("bookmarks", {
                          keyword, true);
 
             let item = keywords[keyword];
-            if (item && item.url.indexOf("%s") > -1)
+            if (item && item.url.contains("%s"))
                 context.fork("keyword/" + keyword, keyword.length + space.length, null, function (context) {
                     context.format = history.format;
                     context.title = [/*L*/keyword + " Quick Search"];
@@ -669,7 +669,7 @@ var Bookmarks = Module("bookmarks", {
                         return history.get({ uri: util.newURI(begin), uriIsPrefix: true }).map(function (item) {
                             let rest = item.url.length - end.length;
                             let query = item.url.substring(begin.length, rest);
-                            if (item.url.substr(rest) == end && query.indexOf("&") == -1)
+                            if (item.url.substr(rest) == end && query.contains("&"))
                                 try {
                                     item.url = decodeURIComponent(query.replace(/#.*/, "").replace(/\+/g, " "));
                                     return item;
@@ -718,14 +718,14 @@ var Bookmarks = Module("bookmarks", {
                     return;
 
                 let words = ctxt.filter.toLowerCase().split(/\s+/g);
-                ctxt.completions = ctxt.completions.filter(i => words.every(w => i.toLowerCase().indexOf(w) >= 0));
+                ctxt.completions = ctxt.completions.filter(i => words.every(w => i.toLowerCase().contains(w)));
 
                 ctxt.hasItems = ctxt.completions.length;
                 ctxt.incomplete = true;
                 ctxt.cache.request = bookmarks.getSuggestions(name, ctxt.filter);
                 ctxt.cache.request.then(function (compl) {
                     ctxt.incomplete = false;
-                    ctxt.completions = array.uniq(ctxt.completions.filter(c => compl.indexOf(c) >= 0)
+                    ctxt.completions = array.uniq(ctxt.completions.filter(c => compl.contains(c))
                                                       .concat(compl), true);
                 }, Cu.reportError);
             });
diff --git a/common/content/dactyl.js b/common/content/dactyl.js
index 080d9495..e4c48d04 100644
--- a/common/content/dactyl.js
+++ b/common/content/dactyl.js
@@ -136,14 +136,14 @@ var Dactyl = Module("dactyl", XPCOM(Ci.nsISupportsWeakReference, ModuleBase), {
                     && !item.hidden
                     && !/rdf:http:/.test(item.getAttribute("label"))) { // FIXME
                     item.dactylPath = parent + item.getAttribute("label");
-                    if (!targetPath || targetPath.indexOf(item.dactylPath) == 0)
+                    if (!targetPath || targetPath.startsWith(item.dactylPath))
                         items.push(item);
                 }
                 else {
                     let path = parent;
                     if (item.localName == "menu")
                         path += item.getAttribute("label") + ".";
-                    if (!targetPath || targetPath.indexOf(path) == 0)
+                    if (!targetPath || targetPath.startsWith(path))
                         addChildren(item, path);
                 }
             }
@@ -459,7 +459,7 @@ var Dactyl = Module("dactyl", XPCOM(Ci.nsISupportsWeakReference, ModuleBase), {
      */
     loadScript: function loadScript(uri, context) {
         let prefix = "literal:" + uri + ":";
-        cache.flush(s => s.indexOf(prefix) == 0);
+        cache.flush(s => s.startsWith(prefix));
         delete literal.files[uri];
         JSMLoader.loadSubScript(uri, context, File.defaultEncoding);
     },
@@ -1147,7 +1147,7 @@ var Dactyl = Module("dactyl", XPCOM(Ci.nsISupportsWeakReference, ModuleBase), {
         if (error instanceof FailedAssertion && error.noTrace || error.message === "Interrupted") {
             let context = contexts.context;
             let prefix = context ? context.file + ":" + context.line + ": " : "";
-            if (error.message && error.message.indexOf(prefix) !== 0 &&
+            if (error.message && !error.message.startsWith(prefix) &&
                     prefix != "[Command Line]:1: ")
                 error.message = prefix + error.message;
 
diff --git a/common/content/editor.js b/common/content/editor.js
index c7f5d59a..942623b7 100644
--- a/common/content/editor.js
+++ b/common/content/editor.js
@@ -764,7 +764,7 @@ var Editor = Module("editor", XPCOM(Ci.nsIEditActionListener, ModuleBase), {
             context = context.fork("registers");
             context.keys = { text: util.identity, description: editor.closure.getRegister };
 
-            context.match = function (r) !this.filter || ~this.filter.indexOf(r);
+            context.match = function (r) !this.filter || this.filter.contains(r);
 
             context.fork("clipboard", 0, this, function (ctxt) {
                 ctxt.match = context.match;
diff --git a/common/content/hints.js b/common/content/hints.js
index 30d72724..d22bfcff 100644
--- a/common/content/hints.js
+++ b/common/content/hints.js
@@ -695,7 +695,7 @@ var HintSession = Class("HintSession", CommandMode, {
     updateValidNumbers: function updateValidNumbers(always) {
         let string = this.getHintString(this.hintNumber);
         for (let hint in values(this.validHints))
-            hint.valid = always || hint.span.getAttribute("number").indexOf(string) == 0;
+            hint.valid = always || hint.span.getAttribute("number").startsWith(string);
     },
 
     tab: function tab(previous) {
@@ -1071,7 +1071,7 @@ var Hints = Module("hints", {
                 mappings.popCommand();
             },
             onChange: function (arg) {
-                if (Object.keys(hints.modes).some(m => m != arg && m.indexOf(arg) == 0))
+                if (Object.keys(hints.modes).some(m => m != arg && m.startsWith(arg)))
                     return;
 
                 this.accepted = true;
diff --git a/common/content/mappings.js b/common/content/mappings.js
index ca18742e..2ba1c7c5 100644
--- a/common/content/mappings.js
+++ b/common/content/mappings.js
@@ -714,6 +714,7 @@ var Mappings = Module("mappings", {
         function uniqueModes(modes) {
             let chars = [k for ([k, v] in Iterator(modules.modes.modeChars))
                          if (v.every(mode => modes.indexOf(mode) >= 0))];
+
             return array.uniq(modes.filter(m => chars.indexOf(m.char) < 0)
                                    .map(m => m.name.toLowerCase())
                                    .concat(chars));
diff --git a/common/modules/buffer.jsm b/common/modules/buffer.jsm
index d8f0490a..7a9247a9 100644
--- a/common/modules/buffer.jsm
+++ b/common/modules/buffer.jsm
@@ -1152,7 +1152,7 @@ var Buffer = Module("Buffer", {
             else {
                 let url = loc || doc.location.href;
                 const PREFIX = "view-source:";
-                if (url.indexOf(PREFIX) == 0)
+                if (url.startsWith(PREFIX))
                     url = url.substr(PREFIX.length);
                 else
                     url = PREFIX + url;
diff --git a/common/modules/cache.jsm b/common/modules/cache.jsm
index e334b613..cbf2a3f6 100644
--- a/common/modules/cache.jsm
+++ b/common/modules/cache.jsm
@@ -62,7 +62,7 @@ var Cache = Module("Cache", XPCOM(Ci.nsIRequestObserver), {
     }),
 
     parse: function parse(str) {
-        if (~'{['.indexOf(str[0]))
+        if ('{['.contains(str[0]))
             return JSON.parse(str);
         return str;
     },
diff --git a/common/modules/commands.jsm b/common/modules/commands.jsm
index 46a93d6d..ca03051c 100644
--- a/common/modules/commands.jsm
+++ b/common/modules/commands.jsm
@@ -764,7 +764,7 @@ var Commands = Module("commands", {
                 return "";
             }
             // TODO: allow matching of aliases?
-            function cmds(hive) hive._list.filter(cmd => cmd.name.indexOf(filter || "") == 0)
+            function cmds(hive) hive._list.filter(cmd => cmd.name.startsWith(filter || ""))
 
             let hives = (hives || this.userHives).map(h => [h, cmds(h)])
                                                  .filter(([h, c]) => c.length);
@@ -1067,7 +1067,7 @@ var Commands = Module("commands", {
                 if (!onlyArgumentsRemaining) {
                     for (let [, opt] in Iterator(options)) {
                         for (let [, optname] in Iterator(opt.names)) {
-                            if (sub.indexOf(optname) == 0) {
+                            if (sub.startsWith(optname)) {
                                 let count = 0;
                                 let invalid = false;
                                 let arg, quote, quoted;
diff --git a/common/modules/completion.jsm b/common/modules/completion.jsm
index 3cfddce4..b1aa205e 100644
--- a/common/modules/completion.jsm
+++ b/common/modules/completion.jsm
@@ -512,7 +512,7 @@ var CompletionContext = Class("CompletionContext", {
                 filtered.sort(this.compare);
                 if (!this.anchored) {
                     let filter = this.filter;
-                    filtered.sort(function s(a, b) (b.text.indexOf(filter) == 0) - (a.text.indexOf(filter) == 0));
+                    filtered.sort(function s(a, b) b.text.startsWith(filter) - a.text.startsWith(filter));
                 }
             }
 
@@ -549,7 +549,7 @@ var CompletionContext = Class("CompletionContext", {
             var substrings = [text];
         }
         else {
-            var compare = function compare(text, s) text.indexOf(s) >= 0;
+            var compare = function compare(text, s) text.contains(s);
             var substrings = [];
             let start = 0;
             let idx;
@@ -970,7 +970,7 @@ var Completion = Module("completion", {
                 context.generate = function generate_() {
                     return [[k.substr(services.ABOUT.length), ""]
                             for (k in Cc)
-                            if (k.indexOf(services.ABOUT) == 0)];
+                            if (k.startsWith(services.ABOUT))];
                 };
             });
 
@@ -1056,7 +1056,7 @@ var Completion = Module("completion", {
         let contains = String.indexOf;
         if (context.ignoreCase) {
             compare = util.compareIgnoreCase;
-            contains = function contains_(a, b) a && a.toLowerCase().indexOf(b.toLowerCase()) > -1;
+            contains = function contains_(a, b) a && a.toLowerCase().contains(b.toLowerCase());
         }
 
         if (tags)
@@ -1180,7 +1180,7 @@ var Completion = Module("completion", {
                                 .concat([let (name = k.substr(services.AUTOCOMPLETE.length))
                                             ["native:" + name, _("autocomplete.description", name)]
                                          for (k in Cc)
-                                         if (k.indexOf(services.AUTOCOMPLETE) == 0)]),
+                                         if (k.startsWith(services.AUTOCOMPLETE))]),
 
                 setter: function setter(values) {
                     if (values.length == 1 && !hasOwnProperty(values[0], this.values)
diff --git a/common/modules/downloads.jsm b/common/modules/downloads.jsm
index 9341e5b1..6e1c6286 100644
--- a/common/modules/downloads.jsm
+++ b/common/modules/downloads.jsm
@@ -20,7 +20,7 @@ var MAX_LOAD_TIME = 10 * 1000;
 let prefix = "DOWNLOAD_";
 var states = iter([v, k.slice(prefix.length).toLowerCase()]
                   for ([k, v] in Iterator(Ci.nsIDownloadManager))
-                  if (k.indexOf(prefix) == 0))
+                  if (k.startsWith(prefix)))
                 .toObject();
 
 var Download = Class("Download", {
@@ -288,7 +288,7 @@ var DownloadList = Class("DownloadList",
     addDownload: function addDownload(download) {
         if (!this.downloads.has(download)) {
             download = Download(download, this);
-            if (this.filter && download.displayName.indexOf(this.filter) === -1)
+            if (this.filter && !download.displayName.contains(this.filter))
                 return;
 
             this.downloads.set(download.download, download);
diff --git a/common/modules/finder.jsm b/common/modules/finder.jsm
index 738b1777..2aa1f40d 100644
--- a/common/modules/finder.jsm
+++ b/common/modules/finder.jsm
@@ -1,4 +1,4 @@
-// Copyright (c) 2008-2013 Kris Maglione <maglione.k@gmail.com>
+// Copyright (c) 2008-2014 Kris Maglione <maglione.k@gmail.com>
 //
 // This work is licensed for reuse under an MIT license. Details are
 // given in the LICENSE.txt file included with this file.
@@ -626,7 +626,7 @@ var RangeFind = Class("RangeFind", {
         if (!this.matchCase)
             pattern = pattern.toLowerCase();
 
-        if (!again && (pattern === "" || pattern.indexOf(this.lastString) !== 0 || this.backward)) {
+        if (!again && (pattern === "" || !pattern.startsWith(this.lastString) || this.backward)) {
             if (!private_)
                 this.range.deselect();
             if (pattern === "")
diff --git a/common/modules/help.jsm b/common/modules/help.jsm
index eca255ba..cc66a595 100644
--- a/common/modules/help.jsm
+++ b/common/modules/help.jsm
@@ -325,7 +325,7 @@ var Help = Module("Help", {
                         }
                         if (name == "href") {
                             value = node.href || value;
-                            if (value.indexOf("dactyl://help-tag/") == 0) {
+                            if (value.startsWith("dactyl://help-tag/")) {
                                 try {
                                     let uri = services.io.newChannel(value, null, null).originalURI;
                                     value = uri.spec == value ? "javascript:;" : uri.path.substr(1);
diff --git a/common/modules/javascript.jsm b/common/modules/javascript.jsm
index 58b24017..a5a3f64b 100644
--- a/common/modules/javascript.jsm
+++ b/common/modules/javascript.jsm
@@ -348,7 +348,7 @@ var JavaScript = Module("javascript", {
         else {
             base.quote = [last, text => util.escapeString(text, ""), last];
             if (prefix)
-                base.filters.push(item => item.item.indexOf(prefix) === 0);
+                base.filters.push(item => item.item.startsWith(prefix));
         }
 
         if (!compl) {
diff --git a/common/modules/overlay.jsm b/common/modules/overlay.jsm
index 4a2470bc..b1f1cab7 100644
--- a/common/modules/overlay.jsm
+++ b/common/modules/overlay.jsm
@@ -358,7 +358,7 @@ var Overlay = Module("Overlay", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReferen
                 delete desc.writable;
                 desc.get = function get() value;
                 desc.set = function set(val) {
-                    if (!callable(val) || Function.prototype.toString(val).indexOf(sentinel) < 0)
+                    if (!callable(val) || !Function.prototype.toString(val).contains(sentinel))
                         Class.replaceProperty(this, k, val);
                     else {
                         let package_ = util.newURI(Components.stack.caller.filename).host;
diff --git a/common/modules/prefs.jsm b/common/modules/prefs.jsm
index 47fec508..c3b53daa 100644
--- a/common/modules/prefs.jsm
+++ b/common/modules/prefs.jsm
@@ -1,6 +1,6 @@
 // Copyright (c) 2006-2008 by Martin Stubenschrott <stubenschrott@vimperator.org>
 // Copyright (c) 2007-2011 by Doug Kearns <dougkearns@gmail.com>
-// Copyright (c) 2008-2013 Kris Maglione <maglione.k@gmail.com>
+// Copyright (c) 2008-2014 Kris Maglione <maglione.k@gmail.com>
 //
 // This work is licensed for reuse under an MIT license. Details are
 // given in the LICENSE.txt file included with this file.
@@ -398,7 +398,7 @@ var Prefs = Module("prefs", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference])
         function prefs() {
             for (let [, pref] in Iterator(prefArray)) {
                 let userValue = services.pref.prefHasUserValue(pref);
-                if (onlyNonDefault && !userValue || pref.indexOf(filter) == -1)
+                if (onlyNonDefault && !userValue || !pref.contains(filter))
                     continue;
 
                 let value = this.get(pref);
diff --git a/common/modules/sanitizer.jsm b/common/modules/sanitizer.jsm
index dbb27894..1c59c4b6 100644
--- a/common/modules/sanitizer.jsm
+++ b/common/modules/sanitizer.jsm
@@ -399,7 +399,7 @@ var Sanitizer = Module("sanitizer", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakRef
         for (let c in iter(services.cookies, Ci.nsICookie2))
             if (!host || util.isSubdomain(c.rawHost, host) ||
                     c.host[0] == "." && c.host.length < host.length
-                        && host.indexOf(c.host) == host.length - c.host.length)
+                        && host.endsWith(c.host))
                 yield c;
 
     },
@@ -597,7 +597,7 @@ var Sanitizer = Module("sanitizer", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakRef
     completion: function initCompletion(dactyl, modules, window) {
         modules.completion.visibleHosts = function completeHosts(context) {
             let res = util.visibleHosts(window.content);
-            if (context.filter && !res.some(host => host.indexOf(context.filter) >= 0))
+            if (context.filter && !res.some(host => host.contains(context.filter)))
                 res.push(context.filter);
 
             context.title = ["Domain"];
diff --git a/common/modules/styles.jsm b/common/modules/styles.jsm
index 29801088..41a67a3b 100644
--- a/common/modules/styles.jsm
+++ b/common/modules/styles.jsm
@@ -212,7 +212,7 @@ var Hive = Class("Hive", {
             name = null;
         }
 
-        if (filter && filter.indexOf(",") > -1)
+        if (filter && filter.contains(","))
             return filter.split(",").reduce(
                 (n, f) => n + this.removeSheet(name, f, index), 0);
 
diff --git a/common/modules/util.jsm b/common/modules/util.jsm
index f7f41529..ca69b092 100644
--- a/common/modules/util.jsm
+++ b/common/modules/util.jsm
@@ -482,7 +482,7 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
                 return obj.res;
             }
 
-            if (pattern.indexOf("{") == -1)
+            if (!pattern.contains("{"))
                 return [pattern];
 
             let res = [];
@@ -516,7 +516,7 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
             rec([]);
             return res;
         }
-        catch (e if e.message && ~e.message.indexOf("res is undefined")) {
+        catch (e if e.message && e.message.contains("res is undefined")) {
             // prefs.safeSet() would be reset on :rehash
             prefs.set("javascript.options.methodjit.chrome", false);
             util.dactyl.warn(_(UTF8("error.damnYouJägermonkey")));
@@ -544,7 +544,7 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
      * @returns {string}
      */
     dequote: function dequote(pattern, chars)
-        pattern.replace(/\\(.)/, (m0, m1) => chars.indexOf(m1) >= 0 ? m1 : m0),
+        pattern.replace(/\\(.)/, (m0, m1) => chars.contains(m1) ? m1 : m0),
 
     /**
      * Returns the nsIDocShell for the given window.
@@ -1110,9 +1110,9 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
 
         function rec(data, level, seen) {
             if (isObject(data)) {
-                if (~seen.indexOf(data))
+                seen = RealSet(seen);
+                if (seen.add(data))
                     throw Error("Recursive object passed");
-                seen = seen.concat([data]);
             }
 
             let prefix = level + INDENT;
@@ -1160,7 +1160,7 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
         }
 
         let res = [];
-        rec(data, "", []);
+        rec(data, "", RealSet());
         return res.join("");
     },