--- a/toolkit/components/extensions/ExtensionContent.jsm
+++ b/toolkit/components/extensions/ExtensionContent.jsm
@@ -325,31 +325,33 @@ class ExtensionContext extends BaseConte
         throw new Error("Invalid target window for this extension context");
       }
       // This is an iframe with content script API enabled and its principal should be the
       // contentWindow itself. (we create a sandbox with the contentWindow as principal and with X-rays disabled
       // because it enables us to create the APIs object in this sandbox object and then copying it
       // into the iframe's window, see Bug 1214658 for rationale)
       this.sandbox = Cu.Sandbox(contentWindow, {
         sandboxPrototype: contentWindow,
+        sameZoneAs: contentWindow,
         wantXrays: false,
         isWebExtensionContentScript: true,
       });
     } else {
       // This metadata is required by the Developer Tools, in order for
       // the content script to be associated with both the extension and
       // the tab holding the content page.
       let metadata = {
         "inner-window-id": this.innerWindowID,
         addonId: attrs.addonId,
       };
 
       this.sandbox = Cu.Sandbox(principal, {
         metadata,
         sandboxPrototype: contentWindow,
+        sameZoneAs: contentWindow,
         wantXrays: true,
         isWebExtensionContentScript: true,
         wantExportHelpers: true,
         wantGlobalProperties: ["XMLHttpRequest", "fetch"],
         originAttributes: attrs,
       });
 
       Cu.evalInSandbox(`