Hi Leo,
Thanks for the questions, I can forward these on to the user, appreciated.
I have installed the most recent version of Firefox myself and am unable to reproduce the issue.
I will forward your questions/suggestions of things to look at and see what I hear back - thanks, appreciated 
Update
Firefox version : 57.0.2 (64 bit)
Log - https://snag.gy/XtUvcC.jpg
I gave the user the link to the Mozilla Discourse instance, whilst they don’t offer a Facebook social login, all of the other options appeared.
Looks like some issues from the screen capture provided above.
They aren’t able to restart the browser just get due to some work. Commitments but have said they will do so as soon as possible and come back to me.
Any thoughts from the above @LeoMcA?
Further Update
He user came back to me a little quicker than I expected.
Disabling the plugins resolved the issue, specifically it turned out to be adBloc Plus.
Thanks for your help Leo, I have learnt something new today which I can use in the future to support our users, appreciated.