firebase data are not displayed by innerHtml =

Im starting to a project and want to use firebase database to store data. Im able to save and load data but cant display them in the html page. Im javaScript newbie, so I cant really see whats wrong.

function loadArticle(articleId) {
            return firebase.database().ref('/articles/' + articleId)
                .once('value', function(snapshot) {
                    console.log(snapshot.val().headline);
                    console.log(document.getElementById("headline") != null);

                    document.getElementById("headline").innerHtml = snapshot.val().headline;
                    document.getElementById("article").innerHtml = snapshot.val().text;
                });
        }

Data is loaded and headline element is not null, but its text is not changed.