Incorrect table display in Firefox and IE, why?

Question

Cross browser

There is a table on the page. Stretching at 100% width. In Chrome and Opera it is displayed correctly. And in Firefox and IE - it's terrible, different lines - different widths (some lines - stretch by 100%, some are squeezed under the content), despite the specified widths for EACH cell as a percentage ... And the merged cells do not understand at all , which should stretch over the entire line (also shrink under the content). Here is an example structure:

<table class="cena_table" border="1px" width="100%">
   <tr class="cena_name">
      <td class="cena_name2" width="50%">НАИМЕНОВАНИЕ РАБОТ</td>
      <td class="cena_name3" width="20%">Единицы измерения</td>
      <td class="cena_name4" width="30%">ЦЕНА, руб.</td>
   </tr>
   <tr>
      <td width="50%">Выезд специалиста и составление сметы</td>
      <td class="center_text" width="20%">количество выездов</td>
      <td width="30%">бесплатно</td>
   </tr>
   <tr>
      <td width="50%">Расчет необходимого количества стройматериалов</td>
      <td class="center_text" width="20%">нет</td>
      <td width="30%">бесплатно</td>
   </tr>
   <tr class="cena3" width="100%">
      <td class="center_text" colspan="3"  width="100%">ПОДГОТОВКА К РЕМОНТУ</td>
   </tr>
   <tr width="100%">
      <td width="50%">Передвинем и вынесем мебель</td>
      <td class="center_text" width="20%">нет</td>
      <td width="30%">договорная</td>
   </tr>
   <tr>
      <td width="50%">Защита мебели полиэтиленовой пленкой</td>
      <td class="center_text" width="20%">нет</td>
      <td width="30%">договорная</td>
   </tr>
   <tr class="cena3" width="100%">
      <td class="center_text" colspan="3" width="100%">ПОТОЛОК</td>
   </tr>
   <tr class="cena2 center_text">
      <td class="center_text" colspan="3" width="100%">Подготовительные работы</td>
   </tr>
   <tr>
      <td width="50%">Демонтаж потолка подвесного (Армстронг,ГКЛ и пр.)</td>
      <td class="center_text" width="20%">м2</td>
      <td width="30%">100</td>
   </tr>
   <tr>
      <td width="50%">Очистка потолка от водоэмульсионной краски,побелки</td>
      <td class="center_text" width="20%">м2</td>
      <td width="30%">100</td>
   </tr>
   <tr>
      <td width="50%">Оскабливание потолка</td>
      <td class="center_text" width="20%">м2</td>
      <td width="30%">50</td>
   </tr>
   <tr>
      <td width="50%">Снятие старых обоев с потолка,плитки</td>
      <td class="center_text" width="20%">м2</td>
      <td width="30%">80</td>
   </tr>
   <tr>
      <td width="50%">Срубка потолочного плинтуса</td>
      <td class="center_text" width="20%">м/п</td>
      <td width="30%">50</td>
   </tr>
   <tr class="cena2">
      <td class="center_text" colspan="3" width="100%">Монтажные и отделочные работы</td>
   </tr>
</table>

I really want to know what I'm doing wrong???