I tried to find a solution to this thing and I spent a lot of time, but it is almost imposible to me to do that.
The matter: I am using Selenium with Java in Firefox
I have some solution, make a class with a robot put there TAB event keys, then call that class. What it does its like a back to focus to the page. For some razon the page lost focus and never find that botton.
Robot robot;
try {
robot = new Robot();
robot.keyPress(KeyEvent.VK_TAB);
robot.keyRelease(KeyEvent.VK_TAB);
} catch (AWTException e) {e.printStackTrace();}