It's been at least 2 months, and no update from Mozilla on the new Threads url. Mozilla, please add "threads.com" to the site list, otherwise the page will never load, and some people may not know this extension is causing it.

How to add manually (until Mozilla updates/if they ever update it):
1. Go to threads.com
2. Click "Facebook container" under the Add-on button (or toolbar if you placed it there)
3. Click "Allow site in Facebook container"
4. Threads will load