Dynamic text positions differently on browsers

This is a bug with how Firefox handles the text baseline property. You are not doing anything wrong.

View the issue on GitHub:

Text Alignment issues with Firefox · Issue #650 · CreateJS/EaselJS · GitHub

You can add this bit of JavaScript to your project to see if it helps...

var firefox = navigator.userAgent.toLowerCase().indexOf('firefox') > -1;
if (firefox && createjs)
{
  createjs.Text.prototype._drawTextLine = function(ctx, text, y)
  {
  // Adjust text position only if textBaseline is "top"
  if (this.textBaseline === "top")
  {
  var lineHeight = this.lineHeight || this.getMeasuredLineHeight();
  y += lineHeight * 0.3;
  }
  // Chrome 17 will fail to draw the text if the last param is included but null, so we feed it a large value instead:
  if (this.outline) { ctx.strokeText(text, 0, y, this.maxWidth||0xFFFF); }
  else { ctx.fillText(text, 0, y, this.maxWidth||0xFFFF); }
  };
}