Rated 5 out of 5 stars

don't know why current version is not available here - but if you follow the link to the website, there is a Firefox 4.0 compatible version 0.17 available ...

Btw: one of the addons I can't work without ...

This review is for a previous version of the add-on (0.16). 

Version 0.17 available at http://livehttpheaders.mozdev.org/

The version 0.17 should be available here soon. It is currently pending review.