Η Google decided not to allow her installation extensions at browser of Chrome, if they do not originate from the official one Web Store.
Because several extensions that were freely distributed in the Internet they were not tested, so they contain quite a lot 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 third-party extensions are installed, their functionality will stop automatically until they are submitted and approved in the Chrome Web Store.
Source: e-pcmag.gr