No, Firefox did not block anything. Firefox contacted the server, and the server sent back a 7–byte text/plain response containing “Blocked”. Since no encoding

No, Firefox did not block anything. Firefox contacted the server, and the server sent back a 7–byte text/plain response containing “Blocked”. Since no encoding was specified, Firefox guesses and displays “Blocked” on the screen. Hopefully it was in an encoding you could read, but in case it shows up as mojibake or something Firefox also put a warning in the dev console. The warning isn’t for end users, it is for the developer of the site who is wondering why their site shows up as mojibake.