I have the same issue. FF 128.0.0, Somona 14.5, Apple M1 Pro 16 GB 2021.
It works with Chrome 124.0 and Enpass 6.9.3 though.
I guess it's related to how DKB supports FF. I worte a ticket to DKB but didn't get a reply. Maybe you can find out what they do differently in FF than in Chrome.