@-moz-document regexp("https://news.ycombinator.com/(?!threads).*") {
    
      td.ind {
          background:
              linear-gradient(to left, rgba(246,246,240,1) 0px, rgba(246,246,240,1) 14px, rgba(246,246,240,0) 14px),
              repeating-linear-gradient(to right, rgba(0,0,0,0) 0px, rgba(0,0,0,0.03) 39px, rgba(0,0,0,0) 40px),
              repeating-linear-gradient(to right, rgba(0,0,0,0) 0px, rgba(0,0,0,0) 32px, rgba(0,0,0,.01) 39px, rgba(0,0,0,0) 40px);
      }
      
      table.comment-tree td,
      table.comment-tree tr,
      table.comment-tree th,
      table.comment-tree,
      table.comment-tree tbody,
      table.comment-tree table {
          margin: 0 !important;
          padding: 0 !important;
          border-spacing: 0 !important;
      }
      
      table.comment-tree td.default {
          padding: 0.5em 0.5em 1em 0.5em !important;
      }
      
      table.comment-tree td.ind {
          padding: 0 0.5em !important;
      }
      
      div.votearrow { padding-bottom: 3px; background: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' width='12' height='20'><polygon points='0,20 12,20 6,0' style='fill:rgb(179,179,179);stroke:none;' /></svg>") !important; background-size: 12px 20px !important; width: 12px!important; }
    
    }

Bonus: Extra large voting buttons (see the div.votearrow definition).

Screenshot: https://i.imgur.com/XrJEKKe.png