Rated 4 out of 5 stars

Even better than a simple line-numbers would be to make it work with the extension "HTML Validator" (http://users.skynet.be/mgueury/mozilla/).

The validation window shows correctly, but it is blank - it only shows errors & line numbers after opening & closing of the HTML validator options :)

Should these two extension work together correctly, it would be superb.

This review is for a previous version of the add-on (0.3.2010070401).