If you are using the Horizon 1.0.5 Theme or earlier you may have come across a little issue with the mobile view of the site in the Firefox browser. 

When the menu is opened on mobile using the burger style icon:

The menu opens as expected:

 

But when the menu is closed the X icon remains and the user cannot interact with the page:

 

 

Simple Fix

Open the assets/header-drawer.js file and add this line of code around line 106:

   details.removeAttribute('open');

This will ensure that the 'open' attribute is removed from the <details> tag. 

The assets/header-drawer.js file seems to be changing regularly in each version release. Look for the following function:

  /**
   * Close the closest menu or submenu that is open
   *
   * @param {HTMLDetailsElement} details
   */
  #close(details) {

Then find these two lines in the function:

    summary.setAttribute('aria-expanded', 'false');
    details.classList.remove('menu-open');

 

And add the new line of code between:

 

    summary.setAttribute('aria-expanded', 'false');
    details.removeAttribute('open');
    details.classList.remove('menu-open');