refactor: one shared extension-API module, and drive the dApp flows on Firefox (closes #153)

src/shared/phishingDomains.js

@@ -18,6 +18,7 @@
 // its own refresh — see updatePhishingList().
 
 const vendoredConfig = require("./phishingBlocklist.json");
+const { storageLocal } = require("./browserApi");
 
 const BLOCKLIST_URL =
     "https://raw.githubusercontent.com/MetaMask/eth-phishing-detect/main/src/config.json";
@@ -46,18 +47,10 @@ let lastAttemptTime = 0;
 let fetchPromise = null;
 let loadPromise = null;
 
-// Resolved on use rather than captured at module load, so a test can install
-// a stub after requiring the module and so the popup — which has no reason to
-// touch the delta — does not fail to load where the API is absent.
-function storageApi() {
-    if (typeof browser !== "undefined" && browser.storage) {
-        return browser.storage.local;
-    }
-    if (typeof chrome !== "undefined" && chrome.storage) {
-        return chrome.storage.local;
-    }
-    return null;
-}
+// storageLocal() resolves on use rather than at module load, so a test can
+// install a stub after requiring this module, and it returns null where the
+// API is absent — which is why the popup, with no reason to touch the delta,
+// loads fine without it.
 
 /**
  * Sanitise a timestamp read back from storage.
@@ -86,7 +79,7 @@ function sanitizeTimestamp(value) {
  * @returns {Promise<void>}
  */
 async function loadDeltaFromStorage() {
-    const storage = storageApi();
+    const storage = storageLocal();
     if (!storage) return;
     try {
         const result = await storage.get(DELTA_STORAGE_KEY);
@@ -122,7 +115,7 @@ function ensureDeltaLoaded() {
  * @returns {Promise<void>}
  */
 async function saveDeltaToStorage() {
-    const storage = storageApi();
+    const storage = storageLocal();
     if (!storage) return;
     try {
         const data = {