NOTE: in this question I am interested in *discovering the actual method* used by Google to track me -*in my particular case*- and in *exploring eventual ways to circumvent it*. This is completely different from the question [is Google spying on us all](https://security.stackexchange.com/questions/24493/is-google-spying-on-all-of-us). That question is asking "if" Google is tracking users and goes on to talk if that is a correct/acceptable behavior or not.
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ok, here is the situation:

I started noticing the same type of ads following me in various sites: in particular a couple of ads regarding "2000+ Chinese women online" and about "meet Thai girls"...

Now, I find that really strange since my Firefox is set to delete cookies when I exit, and Chrome is always in "incognito" mode. 
I also tried manually delete all offline content, but same result.
Another idea: I tried to reboot my internet modem and I got a different public IP.. but still same result.

* As a tests I went on www.linuxquestions.org with different browsers:

	+ with Firefox I get those ads.
	+ with Chrome I get the same ads.
	+ with Tor browser (tor is an anonimity network) I get DIFFERENT ads,
	about Linux and computers/technology.
	+ with my other laptop, using Internet Explorer, same Thai/Chinese ads.

How do you think is Google managing to follow me?

PS: I have an idea but I would like to hear your opinions first..