This has been going on for a while now. When there are new updates for Firefox add-ons and I start Firefox it's trying to download them but it fails. E.g. the first extension is Firebug. After a while I get a dialog:
Firefox could not install the file at http://releases.mozilla.org/pub/mozilla.org/addons/1843/firebug-1.6.0-fx.xpi because: Download error -228
How can I fix this?