diff --git a/src/content/sync.js b/src/content/sync.js
index 9f82e37..fc38d69 100644
--- a/src/content/sync.js
+++ b/src/content/sync.js
@@ -35,16 +35,20 @@ export class Sync {
     await this.getSync(pref);                               // check storage.sync
   }
 
+  static hasOldData(obj) {
+    // FP v3 OR FP v7
+    return Object.hasOwn(obj, 'settings') || Object.hasOwn(obj, 'foxyProxyEdition');
+  }
+
   static async getSync(pref) {
     if (!pref.sync) { return; }
 
     const syncPref = await browser.storage.sync.get();
 
     // check sync from old version 3-7
-    if (!Object.keys(pref)[0] &&
-      (Object.hasOwn(syncPref, 'settings') || Object.hasOwn(syncPref, 'foxyProxyEdition'))) {
-        Object.keys(syncPref).forEach(i => pref[i] = syncPref[i]);
-        return;
+    if ((!Object.keys(pref)[0] || this.hasOldData(pref)) && this.hasOldData(syncPref)) { // (local has no data OR has old data) AND sync has old data
+      Object.keys(syncPref).forEach(i => pref[i] = syncPref[i]); // set sync data to pref to migrate next in background.js
+      return;
     }
 
     // convert object to array & filter proxies