I just discovered that the temporary solution as described in previous
post #20 seem to hold only for the current browser window which has been
once expanded and bounced up in order to correct the offset, however,
opening a new window or right click on a link and selecting "Open link
in New
I am just confirming this problem exists also on Xubuntu 18.04 and
Firefox with the latest software updates as of to this date.
At some point the Linux OS looses the reference point of the pop-up menu with
respect to the right mouse click courser position, and it becomes permanently
offsetted
