Consider if a theme could accomplish what you want: It seems like they all use firefox under the hood, and if all you want is appearance, you shouldn’t need to change your entire browser. Keeping in mind that a smaller fingerprinting pool is less anonymous, if you care about that.

I haven’t actually used any other than librewolf though, so if switching provides any features you care about, go for it.

This is so cool, yet another great advantage of the Netherlands.

Finding previously existing services is a great idea, thanks for the link. Here’s hoping I don’t get too much spam as a result. (but at least I can block individual customers addresses)

To the extent that you still need to use standard apps, consider disabling your advertising ID. EFF has a guide to this at https://www.eff.org/deeplinks/2022/05/how-disable-ad-id-tracking-ios-and-android-and-why-you-should-do-it-now

This won’t stop google of course. You should probably also install a firewall, like other people here have suggested. And keep in mind, disabling features entirely is different from not using them. For example, if location services is turned off, then even google maps doesn’t know your location (in theory anyway), whereas if it is merely unused then google will still check periodically.