diff --git a/src/js/background/backgroundLogic.js b/src/js/background/backgroundLogic.js
index bbb80a9..438b760 100644
--- a/src/js/background/backgroundLogic.js
+++ b/src/js/background/backgroundLogic.js
@@ -33,6 +33,7 @@ const backgroundLogic = {
 
     browser.permissions.onAdded.addListener(permissions => this.resetPermissions(permissions));
     browser.permissions.onRemoved.addListener(permissions => this.resetPermissions(permissions));
+    backgroundLogic.setSyncExclusion();
 
     // Update Translation in Manifest
     browser.runtime.onInstalled.addListener(this.updateTranslationInManifest);
@@ -504,6 +505,17 @@ const backgroundLogic = {
   cookieStoreId(userContextId) {
     if(userContextId === 0) return "firefox-default";
     return `firefox-container-${userContextId}`;
+  },
+
+  async setSyncExclusion() {    
+    // Default container sync exclude regexp to "^tmp\d+$" to prevent
+    // https://github.com/mozilla/multi-account-containers/issues/1675
+    // https://github.com/stoically/temporary-containers/issues/371
+    // for future users of the MAC + TC combination.
+    const { syncExcludeRegExp } = await browser.storage.local.get("syncExcludeRegExp");
+    if (syncExcludeRegExp === undefined) {
+      browser.storage.local.set({syncExcludeRegExp: "^tmp\\d+$"});
+    }
   }
 };