@-moz-document url(about:newtab)
{
  /* Fix cell sizing. Note: you may need to play around with the values for different numbers of rows and columns */
  /* Currently it works for 3 rows x 4 columns */
  .newtab-cell { width: 22% !important; height: 21% !important; margin-bottom: 16px !important; }

  /* Fix grid sizing */
  #newtab-grid { max-height: 500px !important; max-width: 800px !important; overflow: hidden !important; }

  /* Hide unnecessary elements */
  #newtab-margin-top, #newtab-margin-bottom { display:none !important; }
}