Use Margin Auto and Center to center Float Left Div

use inline-block instead of float left.

<center>
  <div style="margin : auto; text-align: center">
    <a href="#" style="display: -moz-inline-box; display: inline-block; left; margin-right: 10px;">Menu Item 1</a>
    <a href="#" style="display: -moz-inline-box; display: inline-block; margin-right: 10px;">Menu Item 2</a>
    <a href="#" style="display: -moz-inline-box; display: inline-block; margin-right: 10px;">Menu Item 3</a>
  </div>
</center>

Why not use an unordered list? After all, you are creating a list of links.

<ul>
 <li><a href="#">Menu Item 1</a></li>
 <li><a href="#">Menu Item 2</a></li>
 <li><a href="#">Menu Item 3</a></li>
</ul>

li {
  display: inline;
}

ul {
  width: 50%;
  margin: 0 auto;
}

Your code works fine, but the div is 100% wide by default so you won't notice any centering.

Either give the div a width (fixed in pixels or relative in percent) or, if you just want to center the menu items, give the div a text-align setting:

<div style="margin : auto; text-align: center">