If you write a HTML file that is not well-formed, such as tags are not properly nested as shown below.

<pre><td><select>....<select></td></pre>

You will find that the select field on the Firefox browser look like this

To solve the problem, we can simply make tags properly nested.  That is, changing from

<pre><td><select>....<select></td></pre>

 

to

<pre><td><select>...</select></td></pre>

 

Now, we will have the select field look fine on Firefox browser