“close this tree” do not work

[luweitest]

Firefox 52 ESR, tab column is put at the right side, auto-hide. When right click a tab and select "close this tree", only first tab under it is closed, not the whole tree.

[luweitest]

When not in auto-hide mode, closing tree works. And I find a workaround in aoto-hide mode:
afer context menu appears, do not move the mouse, thus the menu will remain there, and use keyboard arrow key to move icon to "close this tree", press Enter.

So the point is this closing tree command needs the context menu present.