http://livehttpheaders.mozdev.org/suggestions.html#c416 Please update this extension to make it compatible with FF3. I enabled it using Nightly Tester Tools, and looks like that it works -- no errors. Mozilla/5.0 (X11; U; Linux i686; ru-RU; rv:1.9a8) Gecko/2007091211 GranParadiso/3.0a8