[rndgermandude]

Right, captivedetect.canonicalURL: http://detectportal.firefox.com/success.txt

Tho that isn't mentioned in the article, and I'd be surprised if mozilla collects any data there (other than something like a hit count).

Of course, there are also the update checks, both for Firefox itself and extensions (both not mentioned in the article either, and probably a bad idea to disable this functionality unless some external source like a package manager does the updating for you).