What is "Block Element"? Can you describe in much more detail what it is you are doing in Firefox and what is going wrong? I mean in enough detail that we can try and do exactly the same series of steps as you and see if we get the same failure.

Ah, are you talking about the "Block Element" that the uBlock Origin add-on adds to the context menu? In that case open uBlock Origin's settings, select the "My Filters" tab, and then try to figure out which filters apply to the site you blocked elements on and delete them.