galen (and anyone else who can understand German), you can watch the original German report here. The reporters pretended to be a big data company and bought anonimized data, which was easily de-anonimized through (user)names used.
Yes I saw about this, my German is nowhere good enough to translate this; but it basically boils down to the once-beloved Web Of Trust (WOT) addon for Firefox / Chrome / IE. Basically it crowd-sourced a safety / trustworthiness rating for each website, letting users rate it out of -- I think -- 5 stars on different factors. This really was a highly recommended plugin back in the days where you had to convince your Mum that Amazon was a trustworthy website. Now, there's problems with the whole idea of sending even just the domains visited back to _any_ company, but it seems the data they collected went further than that, even if they only captured the pages visited on each domain that would still reveal far too much about the users, and in this case it's been proven that you can de-anonymise the addons users through the data captured.
Yeah, the report shows a German woman that they were able to identify. She used to have WOT installed, but they also show her using Adblock Plus and Ghostery - neither of which I fully trust. I wouldn't be surprised if many more addons do something similar. I'm glad uBlock Origin is open source and so far I haven't heard anything bad of Disconnect (which I use to block trackers), but who knows...
Ghostery definitely sells your data, I can't remember if it's under the settings or during install but they do tell the user that they do this. I believe Adblock Plus and uBlock (the old, non-open source one) do this too. Problem is, some browsers do this too; I think Chrome has some DNS protection setting which intercepts your DNS requests and sends them on to Google... though to be fair many people use Google's DNS already hah.
Oh I should note: It has since been removed from the Firefox addon database, but remains available from the Chrome store thingy. Edit: Now removed from both and seems DuckDuckGo had some integration which has also been removed.