The move was not completely unexpected. In a May 2012 thread discussing the changes planned for Chrome 21, a Chromium developer noted that, "Our hope and belief is that this installation mechanism will be sufficiently complex that it will reduce the number of off-store extension installs performed. If it doesn't help, we'll try something else."
The new rules will not affect the "Dev" build of Chrome, the roughest-edged version, or "Canary," an even less-polished browser from the Chromium project, the open-source foundation of Chrome. Web apps will not be affected by the policy change.
Google did not specify which version of Chrome will be the first to require all extensions to originate from the browser's store, but by the company's usual tempo, it will likely be Chrome 33.
As of Friday, Chrome Stable was at version 30, and Beta was at version 31.
Browser extensions can be found at the Chrome Web Store.
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