Just found out that if you use Firefox, by default it lets Google give your browser a unique cookie ID that can never be deleted
If you installed Firefox, and didn't go to Options > Security and unchecked both Block Suspect Sites options, Firefox will set a google.com cookie, that survives deletion. Take a look and see for yourself:
Go to Options > Privacy > Remove Individual Cookies, delete the google.com cookie, then reopen that same menu. It's still there. It's still the same unique ID. You can delete every cookie, you can "refresh" Firefox to remove all settings and extensions, you're still getting it back.
Every google search you've ever done with a single browser profile (Private Browsing aside, presumably, since it doesn't use the non-private cookies) has been recorded under a single ID, regardless of what extensions you use.
This bug ticket was supposedly closed after years of Firefox devs pretending it's no biggie. Like privacy on the web isn't really a thing. And yet, I can reproduce it easily in Firefox 39 on both Windows and Linux.
I don't believe for a second Firefox's devs are stupid enough to buy Google's "we HAVE to set a google.com cookie for the safebrowsing service, it doesn't work otherwise" BS. Any alternative domain could have been used, Google's using google.com for a good fucking reason, to track user searches.
I feel betrayed by Mozilla, but what I don't get is why I hadn't heard of this until I discovered it on my own, while browsing my cookie list. Like why isn't this a big deal in privacy circles. Why do people discuss privacy extensions, but not add "of course, all of this is useless for avoiding Google tracking because they bought a supercookie from Mozilla"?