The module works fine on my Linux laptop with Firefox 60 but I can't configure it on Firefox for Android as the configuration fields are not visible: I can see the labels but not the fields.
Edit: I rotated the screen and added the url of my own wallabag server then clicked on "test url" but nothing happened... (Checked also with app.wallabag.it, nothing happened too)
Version 1.5.0 of the module
Edit2 Also the howto page gives an error:
Server Error

Sorry, something went terribly wrong!
E_WARNING - session_write_close(): write failed: No space left on device (28)


Edit Jan. 17, 2019: Hello, thanks for the answer. Indeed, the help page now works but not the add-on, sadly. Still exactly the same problem: still need to rotate the phone for displaying (at least partially) the parameters and the "test url" link does absolutely nothing even with the app.wallabag.it link.
Furthermore, the help only speaks of a Chrome add-on, not the Firefox one... Is it working on Android Firefox?