manifest.json 是所有採用 WebExtension API 的擴充功能中、唯一一個必須包含的檔案。

它提供了應用程式相關的資訊

主要就是讓網頁可以模擬成一個手機的app來使用，

(在手機的桌面上有一個icon可以按, 按下去後有splash screen)

# tells the browser where your application should start when it is launched

"start_url": "/?utm_source=a2hs"

# hide the address bar and browser chrome.

"display": "standalone"

# enforce a specific orientation

"orientation": "landscape"

# defines the set of URLs that the browser considers to be within your app

"scope": "/maps/"