The option exists to "Install from uploaded file". However, the add-ons I've seen have been XML + supporting files in a ZIP, and this installation method does not seem to support that. I've had to upload using an FTP client. Am I missing something-- is it possible to install an add-on, e.g. Widgets, via this method? If not, I might suggest it? it was a user-friendly way of installing add-ons in SMF. I think it required validating FTP credentials obviously but it was all wrapped up in that zip, easy to manage.