I have the desktop app open.
When I click the web extension button on Firefox, it quickly redirects me to the configuration error page, asking me to enable the web extensions on the settings from my desktop app.
However, I do have it properly configured (see image attached).
Details:
Browser: Firefox 58
OS: Manjaro Cinnamon Build
Enpass desktop: 5.6.5
Enpass for Firefox: 5.5.2