<p>I'm using Chris Pederick's Firefox addon <a href="http://chrispederick.com/work/web-developer/" rel="nofollow noreferrer">"Web Developer 1.1.6"</a>. I get this warning when hitting a certain web page on my site: </p>

<blockquote>
  <p>Unknown property 'MozOpacity'. Declaration dropped.</p>
</blockquote>

<p>What does this mean and how can I fix this on my site?</p>

Are you using
```
mozopacity
```
in your CSS stylesheet? This might be spelled wrong and is thus triggering an error.
You might be looking for
```
-moz-opacity
```
which has been dropped as of Firefox 3.0.