I noticed the firstDirect app didn't work on my new Lumia 950 XL, so I emailed FirstDirect. This is their response:
If it isn't supported soon, I may consider moving banks again, since it's so easy to do these days Thought others might want to know.
10-Dec-2015 14:41
To: yokomoko_chapster@live.co.uk
Re: Windows 10 Mobile
Thank you for your message dated 09-Dec-2015 regarding issues you have encountered using our Mobile App.
I confirm that we do not currently support Windows 10 Mobile for our Mobile App. Our development team are currently looking at this, however I am unable to provide any timescales for when this may change.
Please let us know if you require anything further.
Regards
Ryan Ellis
Digital Support
If it isn't supported soon, I may consider moving banks again, since it's so easy to do these days Thought others might want to know.