If I visit this site (in Bulgarian, so in Cyrillic alphabet, UTF8 encoding): https://shop.ilex.bg/index.php?route=product/product&path=17_42&product_id=102 and expand the dropdown menu on the right, the menu items are displayed in gibberish, not in Bulgarian. Even if they are in Bulgarian when you view source / inspect the <select> in the code. And the currently selected item is displayed as it should as well. That happens on a number of other sites (another example: https://crash.bg/kompyutri-vtora-raka), but not every site I visit. The problem is present in FF only, Chrome / Edge do not have this problem. What's even more weird is that if copy the HTML code (the whole <select>) into a personal page on my own site which runs on wordpress, the contents of <select> show as they should.