I found what I think was the problem for me: From the desktop, I was starting Firefox with the “--no-remote” option. If I remove that option, then it works.

I found what I think was the problem for me: From the desktop, I was starting Firefox with the “--no-remote” option. If I remove that option, then it works. I did not use that option when starting in a terminal, but if I do, then the same problem appears.