Η Google decided not to allow installation extensions at browser of Chrome, if they do not originate from the official one Web Store.
Because several extensions that circulated freely on the Internet were not tested, with enough to contain them malware dangerous for the user, Google will not allow them to be installed.
Now, the only source of installation additives at browser, will be done by Chrome Web Store, where Google guarantees the security of the included extensions.
The beginning was done with the publication Google Chrome 35 for Windows. Note that if you have installed third-party extensions will automatically stop working until they are submitted and approved in the Chrome Web Store.
Source: e-pcmag.gr