Have you configured FB app according to the tutorial: https://docs.oxwall.org/plugin-tuts:facebook-connect ?

Yes.

Note it works with IE.

share your url please

http://pinocchio.skaggbyran.se/
I tried adding Facebook SDK as it seems from a JavaScript error that the FB object is missing.

I'm sorry Gustav, but I don't see any red error "FBCONNECT+JOIN_INCOMPLETE"
I only see the green message. See screenshot. I believe you have not properly translate your language. Please check FB connect translation of yours. For this login_success_msg key

Thanks... very peculiar... I tried a new installation of Firefox and yes, that works! Our regular browsers still show the error though... not sure why. We're working on translating. Thanks. Do you know what a normal setup is, that should be used for testing this site?

I'm sorry Gustav, I'm not sure I understood you. What do you mean by normal setup for testing the site? Please elaborate so we could assist you better.

Quote from Oxwall Software I'm sorry Gustav, I'm not sure I understood you. What do you mean by normal setup for testing the site? Please elaborate so we could assist you better.

The browser and operating system being used.

I could join, like your screenshot, using Chromium, on Mac OS X® but Firefox on Mac OS X® did not work. A moment later I could join with Firefox on Mac OS X® as well. Puzzling... will it stay functional?

I'm sorry but we can easily registered via Firefox on MacOS. See screenshots.

What is the version of your Firefox browser.

45.0.2. The problems went away, not sure what happened.