Me.dium, a browser plug-in that connects web users based on visits to the same sites, has raised $15 million in its second round of financing, Venturebeat reports. The round was led by Commonwealth Venture Partners. Other participants included previous backers Spark Capital, Appian Ventures, and independent investor, Brad Feld, as well as several smaller investors. While the amount seems surprisingly large for a downloadable plug-in with a relatively small user base of 15,000, the Boulder, CO-based company’s technology, which allows it to track individuals’ online habits, might be justifiable given the opportunities it could eventually provide to advertisers. Me.dium closed a $5 million first round funding in last June, said co-founder David Mandell, head of marketing. Release. (The company blog post doesn’t add much but it’s amusing.)