window.getComputedStyle method was returning
null or throwing an exception when the style of the given element cannot be retrieved. Such edge cases can be seen with a hidden
<iframe>, for instance. On Firefox 62 and later, to better align with the CSSOM spec and other browsers’ behaviour, the method will return a
CSSStyleDeclaration object which has
0 for the
length property and an empty string for every declaration.
Update: This change breaks Zyxel.com where dropdown menus are wrongly positioned.