Apparently it is the "Turbo" checkbox, which seems to turn the browser into an Opera Mini. How about a little bit of information when enabling this? I don't even remember doing it, must have been a complete accident.

Using Opera on LMDE2, after toying around with my VPN, which probably messed up connectivity for a while, requests sent by my local Opera come from addresses owned by Opera. It is clearly forcing some sort of proxy server while maintaining the browser string.

107.167.113.32 - - [21/Jan/2016:02:36:35 +0100] "GET / HTTP/1.1" 200 1720 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.73 Safari/537.36 OPR/34.0.2036.25"

190.100.96.30 - - [21/Jan/2016:02:36:11 +0100] "GET / HTTP/1.1" 200 1720 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.73 Safari/537.36 OPR/34.0.2036.25"

141.0.13.214 - - [21/Jan/2016:02:34:55 +0100] "GET / HTTP/1.1" 200 1720 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.73 Safari/537.36 OPR/34.0.2036.25"

These seem to belong to the opera mini cluster. Why would you be spying on my web traffic?

Right, third party social plugins would require them, which really touches on the reason to disable them: due to the use of third party cookies, the owners of these plugins can track people across websites, which is really the point behind many of these.

There are less intrusive ways to build these, but I guess you're right: it's too late to go back now and we'll just have to accept that Facebook, Twitter, Google, etc. all know people's web history.

Which site uses them for anything beyond cross-site tracking? I have disabled them the moment I realized they were permitted and had zero problems.

I can't think of a situation where a site would really need them.

I was quite surprised when I recently discovered that third party cookies are accepted by Chromium. They were considered an unacceptable breach of privacy in the not too distant past. They really serve no other purpose than enabling the Internet's top dogs to track people across websites wherever they have ads, a like button, or a similar piece of Javascript.

I can understand why Google isn't interested in disabling third party cookies by default, but you guys surely have no reason to allow such nonsense.