User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:76.0) Gecko/20100101 Firefox/76.0

Steps to reproduce:

Inspecting a custom listbox (eg. https://www.w3.org/TR/wai-aria-practices-1.2/examples/listbox/listbox-scrollable.html) in the accessibility inspector
Selecting one of the options in the listbox
Opening the relations list in the sidebar

Actual results:

The relations list does not show the ARIA activedescendant relation.

Expected results:

The relations list shows the ARIA activedescendant relation.
This would be very helpful when implementing a custom listbox, to quickly verify whether the attributes were set correctly.