diff --git a/src/js/background/assignManager.js b/src/js/background/assignManager.js
index 032adb1fe..d2aa80488 100644
--- a/src/js/background/assignManager.js
+++ b/src/js/background/assignManager.js
@@ -705,9 +705,8 @@ window.assignManager = {
       return browser.tabs.create({url, cookieStoreId, index, active, openerTabId});
     } else {
       let confirmUrl = `${loadPage}?url=${this.encodeURLProperty(url)}&cookieStoreId=${cookieStoreId}`;
-      let currentCookieStoreId;
-      if (currentUserContextId) {
-        currentCookieStoreId = backgroundLogic.cookieStoreId(currentUserContextId);
+      const currentCookieStoreId = backgroundLogic.cookieStoreId(currentUserContextId);
+      if (parseInt(currentUserContextId, 10) > 0) {
         confirmUrl += `&currentCookieStoreId=${currentCookieStoreId}`;
       }
       return browser.tabs.create({
diff --git a/src/js/background/backgroundLogic.js b/src/js/background/backgroundLogic.js
index 76432216d..d0ef360cf 100644
--- a/src/js/background/backgroundLogic.js
+++ b/src/js/background/backgroundLogic.js
@@ -32,6 +32,9 @@ const backgroundLogic = {
     if (!cookieStoreId) {
       return false;
     }
+    if (cookieStoreId === "firefox-default") {
+      return "0";
+    }
     const container = cookieStoreId.replace("firefox-container-", "");
     if (container !== cookieStoreId) {
       return container;
@@ -357,7 +360,7 @@ const backgroundLogic = {
   },
 
   cookieStoreId(userContextId) {
-    if(userContextId === 0) return "firefox-default";
+    if (parseInt(userContextId, 10) === 0) return "firefox-default";
     return `firefox-container-${userContextId}`;
   }
 };
diff --git a/test/features/assignment.test.js b/test/features/assignment.test.js
index 990f3ffe1..1df0e2696 100644
--- a/test/features/assignment.test.js
+++ b/test/features/assignment.test.js
@@ -73,7 +73,7 @@ describe("Assignment Comfirm Page Feature", function () {
         url: "moz-extension://fake/confirm-page.html?" +
                `url=${encodeURIComponent(url)}` +
                `&cookieStoreId=${this.webExt.tab.cookieStoreId}`,
-        cookieStoreId: undefined,
+        cookieStoreId: "firefox-default",
         openerTabId: null,
         index: 2,
         active: true