Send Mass Mail + HTML inserter for Gmail

{
    "update_url": "https:\/\/clients2.google.com\/service\/update2\/crx",
    "manifest_version": 3,
    "name": "Send Mass Mail + HTML inserter for Gmail",
    "description": "A Gmail Extension",
    "version": "2.2.1",
    "icons": {
        "16": "assets\/icons\/mailbrother_16.png",
        "32": "assets\/icons\/mailbrother_32.png",
        "48": "assets\/icons\/mailbrother_48.png",
        "64": "assets\/icons\/mailbrother_64.png",
        "128": "assets\/icons\/mailbrother_128.png"
    },
    "host_permissions": [
        "https:\/\/mail.google.com\/*"
    ],
    "content_scripts": [
        {
            "matches": [
                "*:\/\/mail.google.com\/*"
            ],
            "js": [
                "inject.js"
            ],
            "run_at": "document_start"
        }
    ],
    "web_accessible_resources": [
        {
            "resources": [
                "main.js",
                "*.css",
                "dependency.*",
                "assets\/js\/gsi_client.js"
            ],
            "matches": [
                "*:\/\/mail.google.com\/*"
            ]
        }
    ]
}