Many of the 2.5 addons make Firefox and Chromium browsers to give warning that the site is not trusted. For example, the magnificient Ivy generator is one of them:
http://wiki.blender.org/index.php/Extensions:2.5/Py/Scripts/Curve/Ivy_Gen
Hopefully some developers take this into account and make sure that downloads are secured. Better yet, it would be awesome if those addons could be seen in (Linux) repositories.