Browser Firefox Quantum

Launching an application on browser Firefox Quantum first prompts for authentication with user name and password for the server.
But my user name contains an umlaut and therefore login will not be accepted.
Another name without an umlaut will be accepted.
There are no problems before with older Firefox versions.

What can iI do?

Excuse me for my bad English I am a German user.

Subject: Sounds like a question for Firefox Quantum support

I’m not sure why the issue, I thought UTF-8 was pervasive, but maybe they’ll patch it up.

Subject: Sounds like a question for Firefox Quantum support

I’m not sure why the issue, I thought UTF-8 was pervasive, but maybe they’ll patch it up.