Prevent Firefox from sending a user-agent string in HTTP requests [closed]

I was recently experimenting with HTTP requests and got curious about user agents. In particular, I’d like to know if it’s possible to prevent a browser (in my case Firefox) from including the user agent string in requests. Now, I know there are extensions that modify the string, but that’s not what I’m looking for. I would like to know if the string can be omitted completely.