button Menu in Firefox 52.9.0 not opening the menu

on a narrow screen (smartphone), the button to open the menu not opening the menu altogether.
I clicked many times in Firefox 52.9.0 (32-bit) but never opened.

<button type=”button” class=”menu-toggle”><span class=”menu-icon”>?</span><span class=”menu-text screen-reader-text”> Menu</span></button>

however works in others
Maxthon 5.2.3.3000
Chromium 39.0.2150.5
Opera 36.0.2130.80
Chrome 42.0.2311.152

I have been using Firefox for many years because Firefox is the best way to render site layouts.
the browser is generally not that old and I do not know in which ones it may not work yet.

Similarly, the button does not work in Firefox for the “Lawyer WP” theme. exactly the same button.
https://wp-themes.com/lawyer-wp/
https://www.ads-software.com/support/topic/after-updating-theme-1-0-1-button-does-not-open-menu-in-firefox/ – my topic
https://www.ads-software.com/themes/lawyer-wp/

I do not insist that you fix it.
i am not working with your theme, just notifying.