For those of you who have accounts, like a Facebook account, and "never use it", don't think you're not being tracked. Facebook affiliates have browser tracking web page bugs everywhere. And unless you've "sandboxed" your browser, and perhaps more, they can figure out that the facebook account you logged into last May is associated with your browsing of affiliate sites X, Y, and Z the rest of the year even if you don't log in to facebook.
Your browser carries identifying information, a digital footprint if you will. Then there's IP address and other information.
Anyway, a useful tidbit if you want to thwart services (at least a bit) from tracking your broader behavior is to use multiple browser profiles.
You can do this with firefox by launching with "firefox -P", and you will be presented with a dialog that lets you create or choose a profile. So, for example, you create one profile for facebook. You only use facebook in _that_ profile, _and nothing else_ in that profile. All cookies or sneakier bits that facebook stores in or gathers from that firefox profile is boxed into that profile.
I still use google, because weaning myself from decades of use of it is problematic. So I have a profile called "Google Spy". That's the only place I use any google services that require a login to google.
I can't say how effective this is in the grand scheme of things, but it's a useful step. When I'm in a non-google profile, there's never any sign it knows me, and that's good. Of course if I'm not using my VPN they could figure it out from my IP address, or other clues.
Unfortunately there's still digital footprint stuff available with different browser profiles. Browser sessions in all firefox profiles are still including headers that identify things about my operating system, for instance, which could provide clues.
Anyway, just raising awareness of a tool to be used. You'll still be spied on, but it's a half measure that can be useful for some shielding.