Great advice here:
http://blog.delaguardia.com.mx/index.php?op=ViewArticle&articleId=28&blogId=1

In FF1.5, if a <tr>’s style is changed from display:none to display:block, the row doesn’t appear correctly; for example, a <textarea> within a <td> might appear very small.

The poor display gets worse if one toggles back and forth; for me, vertical space where the row would normally go kept growing with each toggle.

The external blog entry points out that FF1.5 uses display:table-row for displaying, so one might do this:

  try {
    e.style.display = “table-row”;
  } catch (e) { //for IE, etc
    e.style.display = “block”;
  }