diff --git a/web/genericcom.js b/web/genericcom.js
index df616133a..7ba212447 100644
--- a/web/genericcom.js
+++ b/web/genericcom.js
@@ -21,8 +21,7 @@ import { GenericScripting } from "./generic_scripting.js";
 
 if (typeof PDFJSDev !== "undefined" && !PDFJSDev.test("GENERIC")) {
   throw new Error(
-    'Module "pdfjs-web/genericcom" shall not be used outside ' +
-      "GENERIC build."
+    'Module "pdfjs-web/genericcom" shall not be used outside GENERIC build.'
   );
 }
 
diff --git a/web/preferences.js b/web/preferences.js
index ea1ffd483..d47362bd8 100644
--- a/web/preferences.js
+++ b/web/preferences.js
@@ -21,29 +21,36 @@ import { AppOptions, OptionKind } from "./app_options.js";
  *   or every time the viewer is loaded.
  */
 class BasePreferences {
+  #defaults = Object.freeze(
+    typeof PDFJSDev === "undefined" || !PDFJSDev.test("PRODUCTION")
+      ? AppOptions.getAll(OptionKind.PREFERENCE)
+      : PDFJSDev.eval("DEFAULT_PREFERENCES")
+  );
+
+  #prefs = Object.create(null);
+
+  #initializedPromise = null;
+
   constructor() {
     if (this.constructor === BasePreferences) {
       throw new Error("Cannot initialize BasePreferences.");
     }
-    Object.defineProperty(this, "defaults", {
-      value: Object.freeze(
-        typeof PDFJSDev === "undefined" || !PDFJSDev.test("PRODUCTION")
-          ? AppOptions.getAll(OptionKind.PREFERENCE)
-          : PDFJSDev.eval("DEFAULT_PREFERENCES")
-      ),
-      writable: false,
-      enumerable: true,
-      configurable: false,
-    });
-    this.prefs = Object.create(null);
 
-    this._initializedPromise = this._readFromStorage(this.defaults).then(
+    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("CHROME")) {
+      Object.defineProperty(this, "defaults", {
+        get() {
+          return this.#defaults;
+        },
+      });
+    }
+
+    this.#initializedPromise = this._readFromStorage(this.#defaults).then(
       prefs => {
-        for (const name in this.defaults) {
+        for (const name in this.#defaults) {
           const prefValue = prefs?.[name];
           // Ignore preferences whose types don't match the default values.
-          if (typeof prefValue === typeof this.defaults[name]) {
-            this.prefs[name] = prefValue;
+          if (typeof prefValue === typeof this.#defaults[name]) {
+            this.#prefs[name] = prefValue;
           }
         }
       }
@@ -76,9 +83,15 @@ class BasePreferences {
    *                    have been reset.
    */
   async reset() {
-    await this._initializedPromise;
-    this.prefs = Object.create(null);
-    return this._writeToStorage(this.defaults);
+    await this.#initializedPromise;
+    const prefs = this.#prefs;
+
+    this.#prefs = Object.create(null);
+    return this._writeToStorage(this.#defaults).catch(reason => {
+      // Revert all preference values, since writing to storage failed.
+      this.#prefs = prefs;
+      throw reason;
+    });
   }
 
   /**
@@ -89,16 +102,17 @@ class BasePreferences {
    *                    provided that the preference exists and the types match.
    */
   async set(name, value) {
-    await this._initializedPromise;
-    const defaultValue = this.defaults[name];
+    await this.#initializedPromise;
+    const defaultValue = this.#defaults[name],
+      prefs = this.#prefs;
 
     if (defaultValue === undefined) {
       throw new Error(`Set preference: "${name}" is undefined.`);
     } else if (value === undefined) {
       throw new Error("Set preference: no value is specified.");
     }
-    const valueType = typeof value;
-    const defaultType = typeof defaultValue;
+    const valueType = typeof value,
+      defaultType = typeof defaultValue;
 
     if (valueType !== defaultType) {
       if (valueType === "number" && defaultType === "string") {
@@ -113,8 +127,13 @@ class BasePreferences {
         throw new Error(`Set preference: "${value}" must be an integer.`);
       }
     }
-    this.prefs[name] = value;
-    return this._writeToStorage(this.prefs);
+
+    this.#prefs[name] = value;
+    return this._writeToStorage(this.#prefs).catch(reason => {
+      // Revert all preference values, since writing to storage failed.
+      this.#prefs = prefs;
+      throw reason;
+    });
   }
 
   /**
@@ -124,14 +143,13 @@ class BasePreferences {
    *                    containing the value of the preference.
    */
   async get(name) {
-    await this._initializedPromise;
-    const defaultValue = this.defaults[name],
-      prefValue = this.prefs[name];
+    await this.#initializedPromise;
+    const defaultValue = this.#defaults[name];
 
     if (defaultValue === undefined) {
       throw new Error(`Get preference: "${name}" is undefined.`);
     }
-    return prefValue !== undefined ? prefValue : defaultValue;
+    return this.#prefs[name] ?? defaultValue;
   }
 
   /**
@@ -140,12 +158,11 @@ class BasePreferences {
    *                    the values of all preferences.
    */
   async getAll() {
-    await this._initializedPromise;
+    await this.#initializedPromise;
     const obj = Object.create(null);
 
-    for (const name in this.defaults) {
-      const prefValue = this.prefs[name];
-      obj[name] = prefValue !== undefined ? prefValue : this.defaults[name];
+    for (const name in this.#defaults) {
+      obj[name] = this.#prefs[name] ?? this.#defaults[name];
     }
     return obj;
   }