Sorry, the addons are working fine here. I found this one in http://kb.mozillazine.org/Unable_to_install_themes_or_extensions_-_Firefox
Download Error -228
This error message may be caused by having the Firefox cache disabled. To re-enable:
* Firefox 2 and above: Tools -> Options -> Advanced -> Network
* Firefox 1.5: Tools -> Options -> Privacy -> Cache
Make sure the cache is at least 1 MB (50 MB is the default setting).
On Mac OS, this error can occur if the ~/Library/Caches/TemporaryItems folder is not writable. To change the permissions, context click (right-click) on the "TemporaryItems" folder, choose Get Info and, under Sharing and Permissions, change your user permissions to Read & Write. This problem can be caused by a bug in the WASP extension, which is now fixed in the current version.  
Firewalls or spyware screeners may also cause this issue. If you use the CA firewall, Windows Defender, or the resident option of Spybot S&D ("Teatimer" feature), temporarily disable it to see if your system will now allow the extensions or themes to install .
Failing that, a workaround is to right-click the download link, select "Save Link As..." and download the .xpi or .jar file to your computer. You can then manually install it by dragging the file icon onto an open Firefox window .
Note: The Download Error -228 message may also be seen if the required .xpi or .jar file is not actually present on the server site. You can simply try again at a later time or check other download links on both the same site and a different site, before assuming that your own setup is at fault. 
Another solution is disabling Network Monitor Driver. On Windows XP go to Control Panel, Network Connections, Right click your connection, Properties, uncheck network monitor driver, hit ok.