How to install a private user script in Chrome 21+?

In Chrome 20 and older versions, you could simply open any .user.js file in Chrome and it would prompt you to install the user script.

However, in Chrome 21 and up, it downloads the file instead, and displays a warning at the top saying “Extensions, apps, and user scripts can only be added from the Chrome Web Store”.

The “Learn More” link points to http://support.google.com/chrome_webstore/bin/answer.py?hl=en&answer=2664769, but that page doesn’t say anything about user scripts, only about extensions in .crx format, apps, and themes.

This part sounded interesting:

Enterprise Administrators: You can specify URLs that are allowed to install extensions, apps, and themes directly through the ExtensionInstallSources policy.

So, I ran the following commands, then restarted Chrome and Chrome Canary:

defaults write com.google.Chrome ExtensionInstallSources -array "https://gist.github.com/*"
defaults write com.google.Chrome.canary ExtensionInstallSources -array "https://gist.github.com/*"

Sadly, these settings only seem to affect extensions, apps, and themes (as it says in the text), not user scripts. (I’ve filed a bug asking to make this setting affect user scripts as well.)

Any ideas on how to install a private user script (that I don’t want to add to the Chrome Web Store) in Chrome 21+?

The problem was that gist.github.com’s raw URLs redirect to a different domain. So, we have to use these commands instead:

# Allow installing user scripts via GitHub or Userscripts.org
defaults write com.google.Chrome ExtensionInstallSources -array "https://*.github.com/*" "http://userscripts.org/*"
defaults write com.google.Chrome.canary ExtensionInstallSources -array "https://*.github.com/*" "http://userscripts.org/*"

This works!

Anyway, this seems to be a workaround (thanks to Paul Horn for the hint):

1. Download the user script.
2. Open chrome://chrome/extensions/.
3. Drag and drop the user script file on the page you opened in step 2.

Start Chrome with the --enable-easy-off-store-extension-install switch.

To use a command line switch (from Chromium.org):

On Windows:

• Right click on your "Chrome" icon.
• Choose properties
• At the end of your target line, place these parameters: --enable-easy-off-store-extension-install
• It should look like: chrome.exe --enable-easy-off-store-extension-install

On OS X:

• /Applications/Chromium.app/Contents/MacOS/Chromium --enable-easy-off-store-extension-install

• For Google Chrome you'll need to escape spaces like so: /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --enable-easy-off-store-extension-install

On Linux:

• chromium-browser --enable-easy-off-store-extension-install

Well, this took a couple hours of my life to figure out. I guess Google engineers think that we only deserve to install untrusted extensions if we can figure out how to do tricks and jump through their hoops.

The instructions in Mathias's answer look to be spot-on for Mac OS X, but I use Linux. Here's what I did on Linux to enable easier (pre-Chrome-21-style) install of all third-party extensions, apps, and user scripts from any website:

1. Create the policies directory (if it doesn't already exist):

   sudo mkdir -p /etc/opt/chrome/policies/recommended/
   

2. Create the policy file:

   cd /etc/opt/chrome/policies/recommended/
   
   sudo tee easy_install_extensions.json <<EOF
   {
       "ExtensionInstallSources": ["<all_urls>"]
   }
   EOF
   

3. Restart Chrome. Completely exit the program via menu -> Exit; don't just close your current window.

Sources:

• This page recommends drag and drop, which didn't work for me
• Documentation for the relevant policy setting
• Rules for URL match patterns
• How to set Chromium policies on Linux

Notes:

• <all_urls> (used above) is a special pattern according to the URL match docs. Good to know about.
• According to the Linux policy docs, the directories /etc/opt/chrome/policies/{managed,recommended}/ contain JSON policy files. If entries conflict, managed overrides recommended.