Task assigner dropdown bug on Firefox

[4xdk]

Firefox 61.0.1 (doesn't happen on Chrome/Chromium): If right panel contents are higher than the screen (i.e. we can scroll) opening the task assigner dropdown scrolls the sidebar down some 30px.

This seems to happen during the 'onFocus' function in AssignerInput.js.
Click on '@demo'

This could be related to #161 but I'm not quite sure. Either way changing behavior from 'instant' to 'smooth' doesn't affect the bug.

I've tried fixing as per suggestions in SO thread but haven't had much luck with setting 'overflow: hidden' on the scrolled sidebar (it's scrolled and then scroll disappears). The only thing that worked was waiting some 200ms for the scroll to happen and then scrolling with JS. Not ideal.