[frou_dh]

The formal name for the browser is "User Agent".

Your agent should act in you, the user's, interest. Decidedly partisan and so what? You shouldn't have to explicitly instruct it to defend you from surveillance and pollution - it should do that of its own accord from day zero.

Or is your browser a double-agent?

[jfb]

Think about who makes the browser, and what their interests are. Mozilla and Google both are 100% creatures of the advertising world (in the former case, indirectly through their search box deals) and have a vested interest in selling you on.

I'm not saying switch to Safari or Edge, but it's important to remember the incentives that the browser vendors respond to.