diff --git a/background/background.js b/background/background.js
index 80f3f13a..98043d26 100644
--- a/background/background.js
+++ b/background/background.js
@@ -202,7 +202,7 @@ if (chrome.contextMenus) {
       }
       item = Object.assign({id}, item);
       delete item.presentIf;
-      const prefValue = prefs.readOnlyValues[id];
+      const prefValue = prefs.get(id);
       item.title = chrome.i18n.getMessage(item.title);
       if (!item.type && typeof prefValue === 'boolean') {
         item.type = 'checkbox';
@@ -230,7 +230,7 @@ if (chrome.contextMenus) {
   };
 
   const keys = Object.keys(contextMenus);
-  prefs.subscribe(keys.filter(id => typeof prefs.readOnlyValues[id] === 'boolean'), toggleCheckmark);
+  prefs.subscribe(keys.filter(id => typeof prefs.get(id) === 'boolean'), toggleCheckmark);
   prefs.subscribe(keys.filter(id => contextMenus[id].presentIf), togglePresence);
   createContextMenus(keys);
 }
@@ -309,7 +309,7 @@ window.addEventListener('storageReady', function _() {
     window.API_METHODS.getStylesForFrame = enabled ? getStylesForFrame : getStyles;
   };
   prefs.subscribe(['exposeIframes'], updateAPI);
-  updateAPI(null, prefs.readOnlyValues.exposeIframes);
+  updateAPI(null, prefs.get('exposeIframes'));
 }
 
 // *************************************************************************
@@ -317,7 +317,7 @@ window.addEventListener('storageReady', function _() {
 function webNavigationListener(method, {url, tabId, frameId}) {
   Promise.all([
     getStyles({matchUrl: url, asHash: true}),
-    frameId && prefs.readOnlyValues.exposeIframes && getTab(tabId),
+    frameId && prefs.get('exposeIframes') && getTab(tabId),
   ]).then(([styles, tab]) => {
     if (method && URLS.supported(url) && tabId >= 0) {
       if (method === 'styleApply') {
diff --git a/background/util.js b/background/util.js
new file mode 100644
index 00000000..7b85af96
--- /dev/null
+++ b/background/util.js
@@ -0,0 +1,5 @@
+'use strict';
+
+if (typeof localStorage === 'object' && localStorage) {
+  localStorage._BG_ACCESS = 1;
+}
diff --git a/js/messaging.js b/js/messaging.js
index dcbc1dd7..b4b432de 100644
--- a/js/messaging.js
+++ b/js/messaging.js
@@ -97,7 +97,7 @@ if (!BG || BG !== window) {
   BG.API_METHODS = {};
 }
 
-const FIREFOX_NO_DOM_STORAGE = FIREFOX && !tryCatch(() => localStorage);
+const FIREFOX_NO_DOM_STORAGE = FIREFOX && !tryCatch(() => localStorage && localStorage._BG_ACCESS);
 if (FIREFOX_NO_DOM_STORAGE) {
   // may be disabled via dom.storage.enabled
   Object.defineProperty(window, 'localStorage', {value: {}});
diff --git a/js/prefs.js b/js/prefs.js
index b89da994..e92f28dd 100644
--- a/js/prefs.js
+++ b/js/prefs.js
@@ -115,8 +115,7 @@ var prefs = new function Prefs() {
   let broadcastPrefs = {};
 
   Object.defineProperties(this, {
-    defaults: {value: deepCopy(defaults)},
-    readOnlyValues: {value: {}},
+    defaults: {value: deepCopy(defaults)}
   });
 
   Object.assign(Prefs.prototype, {
@@ -154,7 +153,6 @@ var prefs = new function Prefs() {
           break;
       }
       values[key] = value;
-      defineReadonlyProperty(this.readOnlyValues, key, value);
       const hasChanged = !equal(value, oldValue);
       if (!fromBroadcast || FIREFOX_NO_DOM_STORAGE) {
         localStorage[key] = typeof defaults[key] === 'object'
@@ -231,13 +229,9 @@ var prefs = new function Prefs() {
   {
     const importFromBG = () =>
       API.getPrefs().then(prefs => {
-        const props = {};
         for (const id in prefs) {
-          const value = prefs[id];
-          values[id] = value;
-          props[id] = {value: deepCopy(value)};
+          this.set(id, prefs[id], {fromBroadcast: true});
         }
-        Object.defineProperties(this.readOnlyValues, props);
       });
     // Unlike chrome.storage or messaging, HTML5 localStorage is synchronous and always ready,
     // so we'll mirror the prefs to avoid using the wrong defaults during the startup phase
@@ -270,7 +264,6 @@ var prefs = new function Prefs() {
           this.set(key, value, {broadcast: false, sync: false});
         } else {
           values[key] = value;
-          defineReadonlyProperty(this.readOnlyValues, key, value);
         }
       }
       return Promise.resolve();
@@ -404,7 +397,7 @@ var prefs = new function Prefs() {
 // Accepts an array of pref names (values are fetched via prefs.get)
 // and establishes a two-way connection between the document elements and the actual prefs
 function setupLivePrefs(
-  IDs = Object.getOwnPropertyNames(prefs.readOnlyValues)
+  IDs = Object.getOwnPropertyNames(prefs.defaults)
     .filter(id => $('#' + id))
 ) {
   const checkedProps = {};
diff --git a/manage/filters.js b/manage/filters.js
index 24bb8e7b..c1619687 100644
--- a/manage/filters.js
+++ b/manage/filters.js
@@ -114,7 +114,7 @@ onDOMready().then(() => {
       }
       if (value !== undefined) {
         el.lastValue = value;
-        if (el.id in prefs.readOnlyValues) {
+        if (el.id in prefs.defaults) {
           prefs.set(el.id, false);
         }
       }
diff --git a/manage/manage.js b/manage/manage.js
index 01b005f8..9160d18d 100644
--- a/manage/manage.js
+++ b/manage/manage.js
@@ -688,8 +688,8 @@ function highlightEditedStyle() {
 
 
 function usePrefsDuringPageLoad() {
-  for (const id of Object.getOwnPropertyNames(prefs.readOnlyValues)) {
-    const value = prefs.readOnlyValues[id];
+  for (const id of Object.getOwnPropertyNames(prefs.defaults)) {
+    const value = prefs.get(id);
     if (value !== true) continue;
     const el = document.getElementById(id) ||
       id.includes('expanded') && $(`details[data-pref="${id}"]`);
diff --git a/manifest.json b/manifest.json
index 2a6a3ad2..055e4533 100644
--- a/manifest.json
+++ b/manifest.json
@@ -23,6 +23,7 @@
   ],
   "background": {
     "scripts": [
+      "background/util.js",
       "js/messaging.js",
       "js/storage-util.js",
       "js/sections-equal.js",
diff --git a/options/options.js b/options/options.js
index fba0903c..6cbe0054 100644
--- a/options/options.js
+++ b/options/options.js
@@ -57,7 +57,7 @@ document.onclick = e => {
 
     case 'reset':
       $$('input')
-        .filter(input => input.id in prefs.readOnlyValues)
+        .filter(input => input.id in prefs.defaults)
         .forEach(input => prefs.reset(input.id));
       break;
 
diff --git a/package.json b/package.json
index 8ebd7796..07a08b7b 100644
--- a/package.json
+++ b/package.json
@@ -17,7 +17,8 @@
     "semver-bundle": "^0.1.1",
     "stylelint-bundle": "^8.0.0",
     "stylus-lang-bundle": "^0.54.5",
-    "updates": "^4.2.1"
+    "updates": "^4.2.1",
+    "web-ext": "^2.9.1"
   },
   "scripts": {
     "lint": "eslint **/*.js || true",
@@ -27,6 +28,7 @@
     "update-node": "updates -u && node tools/remove-modules.js && npm install",
     "update-codemirror": "node tools/update-libraries.js && node tools/update-codemirror-themes.js",
     "update-versions": "node tools/update-versions",
-    "zip": "npm run update-versions && node tools/zip.js"
+    "zip": "npm run update-versions && node tools/zip.js",
+    "start-firefox": "web-ext run"
   }
 }