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Trying to see if this add-on would be worth installing, I go to its homepage, which is in Russian. It has what looks like a search box for domain names, with the title «Для получения информации введите имя домена или IP-адрес:» which IIUC means "To obtain information enter a domain name or IP address". So I try "addons.mozilla.org" then "mozilla.org" then a few more (none of them in Russia), and the only answer I get (every time) is «Неверно введено имя домена!» which IIUC means "Invalid domain name entered!»