diff --git a/content/buffer.js b/content/buffer.js
index b6c7b263..0b3b43d5 100644
--- a/content/buffer.js
+++ b/content/buffer.js
@@ -1045,7 +1045,7 @@ liberator.Buffer = function () //{{{
         // 0 if loading, 1 if loaded or 2 if load failed
         get loaded()
         {
-            if (typeof window.content.document.pageIsFullyLoaded != "undefined")
+            if (window.content.document.pageIsFullyLoaded !== undefined)
                 return window.content.document.pageIsFullyLoaded;
             else
                 return 0; // in doubt return "loading"
diff --git a/content/events.js b/content/events.js
index 985cefe0..5a5187d5 100644
--- a/content/events.js
+++ b/content/events.js
@@ -361,7 +361,7 @@ liberator.Events = function () //{{{
     function exitPopupMode()
     {
         // gContextMenu is set to NULL by Firefox, when a context menu is closed
-        if (typeof gContextMenu != "undefined" && gContextMenu == null && !activeMenubar)
+        if (gContextMenu !== undefined && gContextMenu == null && !activeMenubar)
             liberator.modes.remove(liberator.modes.MENU);
     }
     function enterMenuMode()
@@ -520,7 +520,7 @@ liberator.Events = function () //{{{
                 {
                     setTimeout(function () {
                         var focused = document.commandDispatcher.focusedElement;
-                        if (focused && (typeof focused.value != "undefined") && focused.value.length == 0)
+                        if (focused && (focused.value !== undefined) && focused.value.length == 0)
                             focused.blur();
                     }, 100);
                 }
@@ -718,7 +718,7 @@ liberator.Events = function () //{{{
             // removeEventListeners() to avoid mem leaks
             liberator.dump("TODO: remove all eventlisteners");
 
-            if (typeof getBrowser != "undefined")
+            if (getBrowser !== undefined)
                 getBrowser().removeProgressListener(this.progressListener);
 
             window.removeEventListener("popupshown", enterPopupMode, true);
diff --git a/content/mail.js b/content/mail.js
index 6742fda2..8269937d 100644
--- a/content/mail.js
+++ b/content/mail.js
@@ -814,9 +814,9 @@ liberator.Mail = function () //{{{
             if (!filter)
                 filter = "";
 
-            if (typeof includeServers == "undefined")
+            if (includeServers === undefined)
                 includeServers = false;
-            if (typeof includeMsgFolders == "undefined")
+            if (includeMsgFolders === undefined)
                 includeMsgFolders = true;
 
             var tree = GetFolderTree();
diff --git a/content/muttator.js b/content/muttator.js
index debc30e4..3e81d687 100644
--- a/content/muttator.js
+++ b/content/muttator.js
@@ -182,7 +182,7 @@ liberator.config = { //{{{
             // XXX: Hack!
             window.document.addEventListener("load", function ()
             {
-                if (typeof window.messageWasEditedExternally == "undefined")
+                if (window.messageWasEditedExternally === undefined)
                 {
                     window.messageWasEditedExternally = false;
                     GetCurrentEditor().addDocumentStateListener(stateListener);
diff --git a/content/options.js b/content/options.js
index 0835adcf..eb7d034f 100644
--- a/content/options.js
+++ b/content/options.js
@@ -109,7 +109,7 @@ liberator.Option = function (names, description, type, defaultValue, extraInfo)
             let tmpValue = newValue;
             newValue = this.setter.call(this, newValue);
 
-            if (typeof newValue == "undefined")
+            if (newValue === undefined)
             {
                 newValue = tmpValue;
                 liberator.log("DEPRECATED: '" + this.name + "' setter should return a value");
@@ -316,7 +316,7 @@ liberator.Options = function () //{{{
                     }
 
                     var expr = liberator.evalExpression(matches[4]);
-                    if (typeof expr == "undefined")
+                    if (expr === undefined)
                     {
                         liberator.echoerr("E15: Invalid expression: " + matches[4]);
                         return;
diff --git a/content/tabs.js b/content/tabs.js
index 41fb09da..aa574bb4 100644
--- a/content/tabs.js
+++ b/content/tabs.js
@@ -884,7 +884,7 @@ liberator.Tabs = function () //{{{
             else
             {
                 buffer = lastBufferSwitchArgs;
-                if (typeof allowNonUnique == "undefined" || allowNonUnique == null)
+                if (allowNonUnique === undefined || allowNonUnique == null) // XXX
                     allowNonUnique = lastBufferSwitchSpecial;
             }