bug Firefox extension doesn't work under Linux

[toto]

I installed Enpass on SolusOS 3 Linux via 3rd party software center. It works properly.

However the Firefox (56.0.2, 64-Bit) Enpass extension (5.5.0.2, 4 Nov 2017) doesn't. When I'm on any login page and click the Enpass extension, it shows me the Enpass Connection Error page instead of filling the fields with the login data:

 

Of course the settings are correct and Enpass is running:

 

This is the output of my lsof -i:10391

Any idea what's wrong?

Thanks for helping me.

Toto