To keep with our principle of simplicity, we decided to take a different approach. Chrome extensions would be simple and single-purpose in nature, and each would only be allowed a single visible UI "surface" in Chrome, a single browser action or page action button. Toolbars wouldn't be supported by design, and users would have more control over which features they added to their browser.
Unfortunately, in some cases, we couldn't enforce these design goals technically. With content scripts, extension developers have full control over the page, so they can put up as much UI as they want, even going as far as to create toolbars in the page. Others used content scripts to create extensions with more subtle features bundled together that were harder to attribute to specific extensions. In many cases, the Chrome Web Store helped by showing poor reviews when users had noticed bad behavior from a particular extension, but in other cases the connection wasn't clear.
Even worse, when extensions were sideloaded locally on their computer (perhaps bundled as part of another piece of software they installed) the user wouldn't have the benefit of the information in the Chrome Web Store at all, so they might not realize they were agreeing to install an extension with unwanted functionality or poor reviews.
It is for these reasons that we've updated the Chrome Web Store policy to enforce our original single-purpose design goal for extensions. We realize that this will require significant changes for some existing extensions. Some may need to be split into multiple separate extensions. Developers may need to switch to a different approach to monetization, which we've recently made easier by adding payment options to extensions. Since these changes may take some time to implement, we're not going to start enforcing the policy for existing extensions in the Web Store until June 2014. For new extensions, the policy will go into effect immediately.
Update May 16, 2014: This will begin being enforced for previously grandfathered extensions (those which were in the Web Store prior to Dec 19, 2013) on July 15, 2014.
