Firefox alignment problem

[lincsimp]

hi
This is the problem page:

http://www.matix.co.uk/readyhelp/demo/

If you view this in firefox you will see that the input and the button are not quite horizontally aligned, as they are in IE. What could be causing this?

<form action="search.php" method="post"  target="mainFrame">
  <div class="main" style="text-align:center"><div class="style1">Type in the word(s) to search for:</div>
    <input name="searchString" type="text" class="input" size="20" />
    <label>
    <input type="submit" class="btn" value="Search" />
    </label>
  </div>
</form>

Cheers

[lincsimp]

fixed!