Time-to-first-byte from Firebase Functions is usually slow (more than 500ms) even without cold start, sometimes (with cold starts) TTFB becomes absolutely unacceptable for projects where performance is important. SSRed HTML is also not Brotli compressed as static files.
This is a really big problem to deploy SSR web apps to Firebase IMO, and cache SWR at the CDN layer (edge) would solve it perfectly.