Because of the difficulties some users have had entirely removing the add-on, and because of the severity of the risk it represents if not disabled, we contacted Microsoft today to indicate that we were looking to disable the extension and plugin for all users via our blocklisting mechanism. Microsoft agreed with the plan, and we put the blocklist entry live immediately. (Some users are already seeing it disabled, less than an hour after we added it!)
Update (Sunday Oct 18, 6:30pm PDT): Microsoft has now confirmed that the Framework Assistant add-on is not a vector for this attack, and we have removed the entry from the blocklist. We are also working on a mechanism to allow Firefox users to re-enable the WPF plugin ahead of its eventual removal from the blocklist. For more information, see Mike Shaver’s latest blog post.