While we can’t speak for all developers, Add to Feedly’s creator, a certain Amit Agarwal, said that he received an email that offered him a four figure pay day for an extension which he states took him only an hour to create. Naturally this sounded like a pretty damn good offer which made him sell the extension to someone else. For a while the extension was left the way it was, but it was only later own did he notice that the new owners had updated the extension to serve ads quietly. It has been speculated that there are other extensions out there who might have sold themselves to ad companies, but as it stands Add to Feedly and Tweet This Page are the ones that have been removed.
If you’re starting to wonder why you are loading more ad websites and experiencing more popups than usual, perhaps disabling your extensions could help you track down the source. Agarwal has since apologized to users for the adware even though it wasn’t technically his fault, and also admitted that it was a bad idea to sell it in the first place.