Some improvements Rated 4 out of 5 stars
Very nice add-on, but it can be better:
1. Add movable icon, some people don't like context menu.
2. This icon should list all source html, js, css (use some separator, lable with number is sufficient). Look for Phoenix add-on (this is done perfectly). We can see gziped and minification source too (it's great).
Check add-on View Source, it has nice icon too, but additionally show css and js inline (what is great) and size for extermal source (approximately). Unfortunately add stupid sidebar (on left side, without off option) and I dont like them.
You use nice formatting code, and if add above option to your add-on it will the best.