diff --git a/src/background.js b/src/background.js
index 7358662..6d5d02d 100644
--- a/src/background.js
+++ b/src/background.js
@@ -14,6 +14,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
+"use strict";
 /* global browser */
 
 let prevStates = new Map();
diff --git a/src/options/options.js b/src/options/options.js
index ebb0086..ba8bdb4 100644
--- a/src/options/options.js
+++ b/src/options/options.js
@@ -14,6 +14,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
+"use strict";
 /* global browser */
 
 document.addEventListener("DOMContentLoaded", async () => {
diff --git a/src/options/options.xhtml b/src/options/options.xhtml
index c01c4ae..341745f 100644
--- a/src/options/options.xhtml
+++ b/src/options/options.xhtml
@@ -23,8 +23,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 		<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
 		<link rel="stylesheet" type="text/css" href="options.css"/>
 		<link rel="stylesheet" type="text/css" href="/browser-style-supplement/extension-options.css"/>
-		<script src="../shared.js"/>
-		<script src="options.js"/>
+		<script type="application/javascript" src="/shared.js"/>
+		<script type="application/javascript" src="options.js"/>
 	</head>
 	<body>
 		<h1 class="browser-style" data-i18n="options_header"/>
diff --git a/src/popup/popup.js b/src/popup/popup.js
index e64fdd2..dc0c0a8 100644
--- a/src/popup/popup.js
+++ b/src/popup/popup.js
@@ -14,6 +14,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
+"use strict";
 /* global browser */
 
 /**
diff --git a/src/popup/popup.xhtml b/src/popup/popup.xhtml
index 56a4379..540a46d 100644
--- a/src/popup/popup.xhtml
+++ b/src/popup/popup.xhtml
@@ -22,8 +22,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 		<title>Application Menu</title>
 		<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
 		<link rel="stylesheet" type="text/css" href="popup.css"/>
-		<script src="../shared.js"/>
-		<script src="popup.js"/>
+		<script type="application/javascript" src="/shared.js"/>
+		<script type="application/javascript" src="popup.js"/>
 	</head>
 	<body>
 		<main id="main" class="panel-section">
diff --git a/src/shared.js b/src/shared.js
index 26b1360..e965079 100644
--- a/src/shared.js
+++ b/src/shared.js
@@ -14,6 +14,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
+"use strict";
 
 /**
  * Gets the default theme for the current browser.
