Prevent Firefox keypress default event, it produced to scroll the page up/down

src/js/plugins/keyboard.js

@@ -68,6 +68,8 @@ export default class Keyboard {
 
     if (method) {
       method.call(this.ws_, argument);
+      // Prevents Firefox key events.
+      event.preventDefault();
     }
   }
 }

static/js/webslides.js

@@ -1816,6 +1816,8 @@ var Keyboard = function () {
 
       if (method) {
         method.call(this.ws_, argument);
+        // Prevents Firefox key events.
+        event.preventDefault();
       }
     }
   }]);