Rated 5 out of 5 stars

This, at least, a non-plus-ultra for me.
Very useful while developing and also sealing on the net to correct on-the-fly wrong IE-oriented code :-(

I made an only little improvement to enlarge the textarea, very small and up to unusable in most cases.
In the sourceditor.js file I modified the textarea style attrib as follows:

position:fixed;
left:100px;
top:100px;
width:800px;
height:600px;
background-color:#ffc;
border:2px solid #c00;
padding:5px;
font-family:verdana,arial,helvetica;
font-size:10px;

of course all in one line to avoid braking the string.

This review is for a previous version of the add-on (0.2b).