Chromium based browsers have non-google sync. Vivaldi implements their own encrypted sync service and I believe Brave does as well.

But I am talking about browser feature support, not stuff that can supplemented with an extension like a password manager.

Firefox has poor support for modern web features including video processing and encoding which makes it very bad at web conferencing/video calls or in-page streaming.

Firefox's developer tools and console is also much worse and missing important features.

Other features Firefox is missing or has poor support for compared to Chromium are WebGPU, WebTransport, Periodic Background Sync, and parts of WebRTC. Plus various APIs for web serial, badging, and Web Share are missing partial or full support.

Firefox still doesn't have functional HDR for images and videos including AV1.

Oh I thought you meant actual chromium browser.

Those seem rather marginal features from my pov but of course once you need them, you need them, I guess.