It was only a matter of time before it happened, because no one checks on Google Chrome store what an extension actually does (because Google says, if an extension has a bad behaviour, users notice it by themselves and give bad reviews… sure… right…). There are many toolbars or extensions for Google Chrome that show the current price of your favorite cryptocurrency: Dogecoins, bitcoin, NXT, and many others.
The problem is that, silently, they spy on the user’s browsing, replacing payment addresse.
For example, on Cryptsy, the address is changed for deposits: in this way you deposit on the wrong account, giving your coins to the fraudster. On bter instead the withdrawal address was changed within a few milliseconds after clicking on OK.
Unfortunately, it is difficult to recognize this kind of scams, it is best to install only the extensions that can be trusted.
On Mozilla Firefox, each extension is controlled by volunteers, but on Chrome nobody controls what is published, that’s the main problem.