Borders not shown in Firefox with border-collapse on table, position: relative on tbody, or background-color on cell

Answer 1

The best way to solve this issue is to do something like this.

Note the position: relative property in the "thead" and the "tbody' elements, those are important. So are the border-collapse and background-clip properties. Works with background-color on all and alternating rows.

table {
  width: 100% !important;
  border-spacing: 0;
  border-collapse: unset !important;

  thead {
    position: relative;
    left: -1px;
    top: -1px;

    tr {
      th {
        background-clip: padding-box;
        border-top: 1px solid #737373!important;
        border-left: 1px solid #737373!important;
        border-right: none !important;
        border-bottom: none !important;

        &:last-child {
          border-right: 1px solid #737373!important;
        }
      }
    }
  }

  tbody {
    position: relative;
    left: -1px;
    top: -1px;

    tr {
      &:last-child {
        td {
          border-bottom: 1px solid #737373!important;
        }
      }

      td {
        background-clip: padding-box;
        border-top: 1px solid #737373!important;
        border-left: 1px solid #737373!important;
        border-right: none !important;
        border-bottom: none !important;

        &:last-child {
          border-right: 1px solid #737373!important;
        }
      }
    }
  }
}