The "short URL" https://bta that we've bookmarked and have used in the past is working as before.
If that link (and/or the BTA button on the firefox toolbar) doesn't work then firefox has probably cached some bogus data. Fix this either by restarting firefox, or choose "Tools:Clear Recent History:Clear Everything" and try again.
For reasons I don't understand this apparently means that the fully-qualified address https://bta.acc.jlab.org (the previous workaround) will break -- don't use that anymore.