When you install an extension from a third-party site (not from Chrome Web Store) by dragging and dropping it onto Chrome extensions page, the browser allows and installs on the first attempt. But after a few seconds, Chrome shows a message from its menu: ‘Unsupported extensions disabled. To make Chrome safer, we disabled some extensions are that aren’t listed in the Chrome Web Store and may have been added without your Knowledge’.
Browser hard disables that extension, you can’t re-enable it. That extension will be grayed out on the extensions page also.
Installing and using an unsupported extension in Chrome Browser
If you forgot, Google browser on Windows no longer allows extension installs outside Web Store. If you desperately want to use that extension any how, follow the workarounds below.
1. Install the extension using developer mode, when you do that, Chrome nags you on every start of browser to disable developer mode extensions, which you can ignore and continue to use the extension.
2. Install that extension in Chrome Canary or Developer (you still need to drag and drop the extension onto the extensions page to install)
Note: You can use Canary and stable versions simultaneously, but not dev. and beta/stable versions, when you install Dev., it replaces the stable version.
So the obvious choice would be Canary, but do remember its on the bleeding edge, can be unstable and crashes at times and consumes more memory when the build is SyZyASan.
3. Ask the developer to publish his extension on the Chrome Web Store, you and other user can still re-enable and use that extension after that.
4. You can install and use that extension on Mac, Linux (in Chrome browser) and Chromebook.
So what you decide in such situation? Let me know in the comments.