diff --git a/ext/bg/js/conditions-ui.js b/ext/bg/js/conditions-ui.js
index a6f54a1c..43c6dc08 100644
--- a/ext/bg/js/conditions-ui.js
+++ b/ext/bg/js/conditions-ui.js
@@ -36,7 +36,7 @@ ConditionsUI.Container = class Container {
 
         this.container.empty();
 
-        for (const conditionGroup of conditionGroups) {
+        for (const conditionGroup of toIterable(conditionGroups)) {
             this.children.push(new ConditionsUI.ConditionGroup(this, conditionGroup));
         }
 
@@ -122,7 +122,7 @@ ConditionsUI.ConditionGroup = class ConditionGroup {
         this.separator = ConditionsUI.instantiateTemplate('#condition-group-separator-template').appendTo(parent.container);
         this.addButton = this.options.find('.condition-add');
 
-        for (const condition of conditionGroup.conditions) {
+        for (const condition of toIterable(conditionGroup.conditions)) {
             this.children.push(new ConditionsUI.Condition(this, condition));
         }
 
diff --git a/ext/bg/js/settings.js b/ext/bg/js/settings.js
index c85cc8a4..9838ea02 100644
--- a/ext/bg/js/settings.js
+++ b/ext/bg/js/settings.js
@@ -425,7 +425,7 @@ async function onDictionaryPurge(e) {
         dictionarySpinnerShow(true);
 
         await utilDatabasePurge();
-        for (const options of await getOptionsArray()) {
+        for (const options of toIterable(await getOptionsArray())) {
             options.dictionaries = utilBackgroundIsolate({});
             options.general.mainDictionary = '';
         }
@@ -474,7 +474,7 @@ async function onDictionaryImport(e) {
 
         const exceptions = [];
         const summary = await utilDatabaseImport(e.target.files[0], updateProgress, exceptions);
-        for (const options of await getOptionsArray()) {
+        for (const options of toIterable(await getOptionsArray())) {
             options.dictionaries[summary.title] = utilBackgroundIsolate({
                 enabled: true,
                 priority: 0,
diff --git a/ext/mixed/js/extension.js b/ext/mixed/js/extension.js
index d7085e5b..5c803132 100644
--- a/ext/mixed/js/extension.js
+++ b/ext/mixed/js/extension.js
@@ -17,13 +17,24 @@
  */
 
 
+// toIterable is required on Edge for cross-window origin objects.
 function toIterable(value) {
     if (typeof Symbol !== 'undefined' && typeof value[Symbol.iterator] !== 'undefined') {
         return value;
     }
 
-    const array = JSON.parse(JSON.stringify(value));
-    return Array.isArray(array) ? array : [];
+    if (value !== null && typeof value === 'object') {
+        const length = value.length;
+        if (typeof length === 'number' && Number.isFinite(length)) {
+            const array = [];
+            for (let i = 0; i < length; ++i) {
+                array.push(value[i]);
+            }
+            return array;
+        }
+    }
+
+    throw 'Could not convert to iterable';
 }
 
 function extensionHasChrome() {