Firefox has still some clear advantages over Brave, thanks to owning their engine.
A trivial example is the battery API. It's nowadays mainly used for tracking, but is an official webstandard. Mozilla decided to fuzzy it, so it lost its usefulness for tracking. Google didn't.
And I imagine, there's hundreds of similar examples at this scale, which as an average user you'll just never hear of.
One bigger feature is Firefox's Containers. It's based on work from the Tor Browser. Which also just illustrates what this partnership sometimes brings forth. Tor Browser is going to always be there, checking the Firefox code for privacy problems, and will suggest better ways of doing things, which Mozilla can just adopt.
For Chromium, there exist in principle similar efforts, like Brave, Iridium Browser, ungoogled-chromium, but these will always fight an uphill battle against Google and obviously Google isn't going to adopt and maintain their fixes.
Why this takes so long is because once such a standard is introduced, you can't take that decision back anymore without breaking a lot of things. They don't want to introduce standards which end up being used only by a small number of people while causing a lot of maintenance-work and then being tied to maintaining it anyways.
That also is the reason why these decisions often happen in the same time frame for different browser vendors. If another browser vendors decides to introduce it, you can be much more sure that you won't be supporting it without anyone using it. And obviously also just to not be left behind by web developers.
A trivial example is the battery API. It's nowadays mainly used for tracking, but is an official webstandard. Mozilla decided to fuzzy it, so it lost its usefulness for tracking. Google didn't.
And I imagine, there's hundreds of similar examples at this scale, which as an average user you'll just never hear of.
One bigger feature is Firefox's Containers. It's based on work from the Tor Browser. Which also just illustrates what this partnership sometimes brings forth. Tor Browser is going to always be there, checking the Firefox code for privacy problems, and will suggest better ways of doing things, which Mozilla can just adopt.
For Chromium, there exist in principle similar efforts, like Brave, Iridium Browser, ungoogled-chromium, but these will always fight an uphill battle against Google and obviously Google isn't going to adopt and maintain their fixes.