Installing Greasemonkey user scripts could not be any easier, usually, but how do you install a .js file which has already been downloaded like, for example, from GitHub, or copied from pastebin?
With Google Chrome’s built-in Greasemonkey support there is no apparent interface to do this, and I cannot find any suitable location in the user directory.
Rename the file to
*.user.js and drag and drop the file to Chrome. It’ll prompt you if you want to proceed with the installation. The script will be converted to a Chrome extension and installed.
Ok, it now says
Extensions, apps, and user scripts can only be added from the Chrome
But you can still drag and drop user scripts or extensions onto
chrome://chrome/extensions/ page aka
Menu — Tools — Extensions.