selectに表示される行の数を制限する

これを試すことができます：

<select name="select1" onmousedown="if(this.options.length>8){this.size=8;}"  onchange='this.size=0;' onblur="this.size=0;">
             <option value="1">This is select number 1</option>
             <option value="2">This is select number 2</option>
             <option value="3">This is select number 3</option>
             <option value="4">This is select number 4</option>
             <option value="5">This is select number 5</option>
             <option value="6">This is select number 6</option>
             <option value="7">This is select number 7</option>
             <option value="8">This is select number 8</option>
             <option value="9">This is select number 9</option>
             <option value="10">This is select number 10</option>
             <option value="11">This is select number 11</option>
             <option value="12">This is select number 12</option>
       </select>