__FIREBASE_DEFAULTS__ not available when app in iframe

### [REQUIRED] Environment info

**firebase-tools:**
12.5.4

**Platform:**
ChromeOS/Linux

### [REQUIRED] Test case

1) Create a starter firebase project w/experimental frameworks (e.g. nextjs or vite)
2) Add a call to initializeApp() with no args.
3) Run the emulators

Load the app in a tab/window, should be OK.

4) Iframe the app, but host the iframe elsewhere
5) Load the outer page

### [REQUIRED] Steps to reproduce

See above

### [REQUIRED] Expected behavior

initializeApp() call is successful.

### [REQUIRED] Actual behavior

initializeApp() fails due to missing configuration.

I suspect this is due to the samesite policy on the __FIREBASE_DEFAULTS__ cookie. In devtools, it has a samesite=strict policy which requires the cookie domain match the URL bar. That makes the config unavailable in the iframe.

Please consider changing to samesite=lax or at least give a way to override it.