diff --git a/webextension/background.js b/webextension/background.js
index 754fd7c..9ac0f85 100644
--- a/webextension/background.js
+++ b/webextension/background.js
@@ -197,6 +197,12 @@ const assignManager = {
 
   async _setOrRemoveAssignment(tabId, pageUrl, userContextId, remove) {
     let actionName;
+
+    // https://github.com/mozilla/testpilot-containers/issues/626
+    // Context menu has stored context IDs as strings, so we need to coerce
+    // the value to a string for accurate checking
+    userContextId = String(userContextId);
+
     if (!remove) {
       await this.storageArea.set(pageUrl, {
         userContextId,