In an effort to curb malware and other misleading software being installed in its Chrome browser, Google will soon limit extension installs to those found in the official Chrome Web Store. Don't worry, though — if you're willing to take the risk, you can still install anything you want.
Extensions are normally found in the Web Store, where a search reveals handy things like email notifiers, ad blockers and weather apps. But some websites also link to associated extensions or offer them for download — and people often install these without a second thought. That's not a problem when it's a Facebook messaging app, but there is plenty of malware out there that gets installed the same way.
Google's solution is to allow by default only extensions that come from the official store — much like how other app stores work. But if you're a developer or know a certain unofficial extension is legit, you can still install anything by checking the "developer mode" box and manually selecting the extension file. (A FAQ is available for those interested.)
The change was first suggested in a blog post several months ago, but the next version of Chrome (33) should actually implement it.