https://thefreethoughtproject.com/
When I select Block element, the yellow highlight will not display. Nevertheless, if you click somewhere, some element is selected and the item filter is displayed in the pop-up menu. I've restarted Firefox and tried it on multiple instances and never is the yellow highlight displayed, even though it is working on other sites.
ABP 3.0.4
Firefox 60.0
(And just a friendly reminder, element blocking still doesn't work at all on Facebook.)