JavaScript definition has wrong indentation.

[AnmAtAnm]

on setTooltip() and setHelpUrl lines.

Blockly.Blocks['myFirstBlock'] = {
  init: function() {
    this.appendStatementInput("NAME")
        .appendField("My Block");
    this.setColour(230);
 this.setTooltip("");                       // This line
 this.setHelpUrl("");                       // And this line
  } 
};

Also true in original demo/blockfactory