know how to edit the HTML code

I have a website and i don’t know how to edit the HTML code in live mode is that possible?
Thank You

AFAIK, no.
if your website is static files, then you have to modify it.

If your web server allows people to come along and change your live files in their browser, well, that would be bad!

But seriously: Some servers enable WebDAV as a method to edit remote files from a browser, but I don’t think Firefox has native support for WebDAV.