Google has been tightening control over its Chrome ecosystem.
In a recent update, the company disabled the ability to install extensions from outside the Web Store.
you’re free to get it back, though, with a simple check box.
However, as reader icedrake523 points out, you could whitelist that extension by following the instructionshere.
Then, when you restart Chrome, you won’t need to manually reactivate the extension.
How to Manually Install Extensions in Google Chrome| Make Tech Easier