http://awoozruja5y3x2s3dsecryqk4bnaxezwxkn6e4mbo3fdkm6odw6brhid.onion/computers/ANON_WebBrowser.php
If they aren't on the default site just search for the terms "firefox, add-on, name of add-on" in your favourite search engine and they should show up as the first couple of links. Extension: BugMeNot ( optional ) Description: Bypass compulsory web registration with the context menu. Purpose: Allows you to bypass compulsory registrations from various free sites.