Pale Moon forum

I am overhauling my Linux Mint install, including a clean install of Pale Moon, which I haven't poked under linux recently. There is an oddity I would like to correct. When I enter Customize mode, icons for Bookmarks and History appear to the right of the Search area, with dropdown indicators. They disappear as soon as I leave Customize mode. There are also icons for both in the unused icons area, which when placed in the toolbar do not disappear, and open the relevant listing in the sidebar. I would prefer the dropdown versions, but I can't find any settings that seem to affect their disappearance.

Anyone know how to make those active?