metamask-extension/docs/add-to-chrome.md

Add Custom Build to Chrome

• Open Settings > Extensions.
• Check "Developer mode".
• Alternatively, use the URL chrome://extensions/ in your address bar
• At the top, click Load Unpacked Extension.
• Navigate to your metamask-plugin/dist/chrome folder.
• Click Select.
• Change to your locale via chrome://settings/languages
• Restart the browser and test the plugin in your locale

You now have the plugin, and can click 'inspect views: background plugin' to view its dev console.