I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

second this

Same issue here. Just installed firebase right now. I hope it will be resolved soon!

same issue while installing the latest [email protected].

Bump

So the good news is that core-js code isn't used in the code for any Firebase SDK products installed through NPM. It was included in @firebase/polyfill package which is currently only bundled into the compat CDN builds (where Firebase is included using script tags, and applying only to urls that end with -compat.js). We forgot to remove it from the dependencies in package.json (which is why it's installing during yarn/npm install) but the code isn't imported into any Firebase code.

NPM users and users of the v9 CDN scripts shouldn't need to worry. I'll remove @firebase/polyfill from the dependencies and you should stop getting that warning after the next release.

As of v9 we've stopped updating @firebase/polyfill and expect users to provide their own so I'll also remove the polyfill import from the compat CDNs.