Unfortunately Firefox doesn't have a replacement for the "Android System WebView" component, so any app that embeds a browser component (and oh boy is that a lot of them) will still be using Chrome.
It should be possible to have a shim that allows Mozilla's "GeckoView" component to implement the API, but - per that ticket, at least - most Android ROMs won't allow alternatives to the Google one.
The Firefox browser is genuinely great, but it's so far from possible to replace Chrome with it everywhere a browser is used.
Other poster was saying apps that are built around web content use Chrome's webviewer component, and that tons of apps these days are react native, or whatever that Apache foundation tool is for deploying web apps as native apps.
Privacy and digital rights are not a binary "use strange hard to use tools or give everything to google." There are things you can do to improve your ability to own your own data. Giving up immediately is letting perfect be the enemy of good. Running Firefox on your google phone will still win you back something