Something has changed between FF 80.0 and 80.0.1! Aug 30 and Sept 03, 2020. Either a change to the code for uBlock Origin, or a change Yahoo made, that doesn't like uBlock now.
On Aug 30, 2020 I could access my contacts normally in Yahoo mail. Now on Sept 03, My contact list is grayed out, until I turn off uBlock, then my contact list appears normally! I STRONGLY suspect yahoo made changes, since the uBlock update preceded this problem!
It may also have to be Off to allow display some web flyers!