[
    {
        "property": "theme.better_uniextbtn.default",
        "label": "Select Button:",
        "type": "dropdown",
        "defaultValue": "Default",
        "options": [
            {
                "label": "Default",
                "value": "Default"
            },
            {
                "label": "Firefox",
                "value": "Firefox"
            },
            {
                "label": "Custom",
                "value": "Custom"
            }
        ]
    },
    {
        "property": "theme.better_uniextbtn.custom",
        "label": "Custom Button: url(url or base64 here)",
        "type": "string",
        "defaultValue": "url(chrome://branding/content/icon32.png)"
    }
]