On Firefox 51.0.1. under Weindows 10, registered user, I have entered wrong sentence on PHP 5. echo excercise, and after error message I entered correct message, but it shows me save and continue button blank. without any text. And it doesn't go to further excercies untill full page refresh and come back to first page. This happened on previous pages again. Any time I make mistake with code it does this.
Replace this line with your code.
echo "I'm learning PHP";