Firefox has the option to "block new requests asking to allow notifications". Just check under Preferences > Privacy & Security > Permissions.
Most sites will show a custom box first, and only if you agree to that box, will they ask the browser to enable notifications. They do it so that they can ask you again if you deny, because responding “deny” to the real browser prompt blocks any future attempts.
Done, thanks! Glad I recently switched over from Chrome to Firefox on most of my systems. :-)
I don’t know about other browsers but you can turn that off inside Firefox‘s privacy settings.