Describe the bug
The Contacts menu is displayed out of screen in fullscreen mode

To Reproduce
Steps to reproduce the behavior:

1. Go to https://jabberfr.org/converse/
2. Click on the hamburger menu to the right of the Contacts list.
3. See that the menu starts much to the left of the left of the browser window.

Expected behavior
This menu would be shifted to the right, so that I could see it entirely and not click blindly on its items to see what they do.

Screenshots

Environment:

• Desktop
• Browser: Firefox
• Converse.js version 12 on commit f71d261.

Additional context
Maybe this requires the locale to be French?