diff --git a/ext/fg/js/document.js b/ext/fg/js/document.js
index 3b4cc28f..6103c7c5 100644
--- a/ext/fg/js/document.js
+++ b/ext/fg/js/document.js
@@ -28,6 +28,9 @@ function docSetImposterStyle(style, propertyName, value) {
 }
 
 function docImposterCreate(element, isTextarea) {
+    const body = document.body;
+    if (body === null) { return [null, null]; }
+
     const elementStyle = window.getComputedStyle(element);
     const elementRect = element.getBoundingClientRect();
     const documentRect = document.documentElement.getBoundingClientRect();
@@ -78,7 +81,7 @@ function docImposterCreate(element, isTextarea) {
     }
 
     container.appendChild(imposter);
-    document.body.appendChild(container);
+    body.appendChild(container);
 
     // Adjust size
     const imposterRect = imposter.getBoundingClientRect();
diff --git a/ext/fg/js/float.js b/ext/fg/js/float.js
index 294093cd..77e8edd8 100644
--- a/ext/fg/js/float.js
+++ b/ext/fg/js/float.js
@@ -162,7 +162,9 @@ class DisplayFloat extends Display {
     }
 
     setContentScale(scale) {
-        document.body.style.fontSize = `${scale}em`;
+        const body = document.body;
+        if (body === null) { return; }
+        body.style.fontSize = `${scale}em`;
     }
 
     async getDocumentTitle() {
diff --git a/ext/fg/js/popup.js b/ext/fg/js/popup.js
index 2b33b714..f5cb6f77 100644
--- a/ext/fg/js/popup.js
+++ b/ext/fg/js/popup.js
@@ -389,8 +389,13 @@ class Popup {
 
     _getSiteColor() {
         const color = [255, 255, 255];
-        Popup._addColor(color, Popup._getColorInfo(window.getComputedStyle(document.documentElement).backgroundColor));
-        Popup._addColor(color, Popup._getColorInfo(window.getComputedStyle(document.body).backgroundColor));
+        const {documentElement, body} = document;
+        if (documentElement !== null) {
+            Popup._addColor(color, Popup._getColorInfo(window.getComputedStyle(documentElement).backgroundColor));
+        }
+        if (body !== null) {
+            Popup._addColor(color, Popup._getColorInfo(window.getComputedStyle(body).backgroundColor));
+        }
         const dark = (color[0] < 128 && color[1] < 128 && color[2] < 128);
         return dark ? 'dark' : 'light';
     }
@@ -575,10 +580,11 @@ class Popup {
             }
         }
 
+        const body = document.body;
         return {
             left: 0,
             top: 0,
-            right: document.body.clientWidth,
+            right: (body !== null ? body.clientWidth : 0),
             bottom: window.innerHeight
         };
     }
diff --git a/ext/mixed/js/dynamic-loader.js b/ext/mixed/js/dynamic-loader.js
index 29672d36..51b6821b 100644
--- a/ext/mixed/js/dynamic-loader.js
+++ b/ext/mixed/js/dynamic-loader.js
@@ -31,8 +31,13 @@ const dynamicLoader = (() => {
     }
 
     function loadScripts(urls) {
-        return new Promise((resolve) => {
+        return new Promise((resolve, reject) => {
             const parent = document.body;
+            if (parent === null) {
+                reject(new Error('Missing body'));
+                return;
+            }
+
             for (const url of urls) {
                 const node = parent.querySelector(`script[src='${escapeCSSAttribute(url)}']`);
                 if (node !== null) { continue; }
@@ -43,12 +48,11 @@ const dynamicLoader = (() => {
                 parent.appendChild(script);
             }
 
-            loadScriptSentinel(resolve);
+            loadScriptSentinel(parent, resolve, reject);
         });
     }
 
-    function loadScriptSentinel(resolve, reject) {
-        const parent = document.body;
+    function loadScriptSentinel(parent, resolve, reject) {
         const script = document.createElement('script');
 
         const sentinelEventName = 'dynamicLoaderSentinel';