That is a problem with that website, but that extension hasn't been updated for Firefox 3.6 or later, so won't work with Firefox 6 anyway.

Maybe try:

• OptimizeGoogle: https://addons.mozilla.org/firefox/addon/optimizegoogle/

For anyone interested, the poster above is referring to the extension CustomizeGoogle. One will receive this error every time Firefox checks for add-on updates, even if it is disabled. Uninstalling the add-on will fix this issue, and OptimizeGoogle, although no longer maintained, is a working alternative.

I had exactly the same problem in appearance and security warning in regard to "godaddy.com" security certificate, however, the solution did not appear to have anything to do with "godaddy.com"

The problem turned out to be an apparently unrelated extension for "Flash Video Downloader"

I Removed it, in the Firefox Add-ons Manager, and had no more problems.