[Quick Note] Why all browsers' user agent header start with "Mozilla" ?

It's a long story.

User Agent Explained: Necessary for Internet Access
https://whatismyipaddress.com/your-user-agent

History of the browser user-agent string
https://webaim.org/blog/user-agent-string-history

為啥所有的瀏覽器都假扮成Mozilla？
https://youtu.be/yYKW5p0gmg8