I don't know of anything that is completely broken, but some functionality requiers chrome:
On Google Docs, paste as markdown, copy and paste from menus, paste without formatting, etc. only works on chrome. This functionality could be done with standard APIs, but instead google uses a hidden, pre-installed extension to implement it.
Offline mode doesn't work on firefox for either gmail or google docs.
Google doodles don't show up on Firefox Mobile, unless you spoof a chrome user agent.
Youtube has repeatedly had serious performance problems on Firefox.
"AI overview" (which I happen to find really useful) was only available on Chrome and Safari for at least a few months.
Sure, it's a lab experiment or whatever, but these are just words, and the effect is that I have to use a different browser to be able to use them, for absolutely no technical reason. (The LLM is running on Google's servers and provides plaintext. I think Firefox could handle that.)
What google site or service requires Chrome?