Normally, we treat the body as the DOM node for a DocAccessible.
However, a click listener can be added to the root element; e.g. the html element.
We now treat a click listener added to the root element the same as if one were added to the body.
This required a change to nsAccessibilityService to use the DocAccessible when click listeners change for the root element so a cache update is pushed.
This change was made for the body also, since we weren't pushing a cache update for click listener changes on the body either.
Differential Revision: https://phabricator.services.mozilla.com/D144278
a3b482acc2