1st problem - it shouldn't matter too much if you paste all of the url or just the end part (as long as it has the access code bit), it will look for the section it needs and use it. Unfortunately I don't have my WM device with me, so hopefully someone can confirm or not if the authorisation is still working (I'll try to test it when I can).Problem with Facebook API. Probably Facebook updated their API stuff..
1st problem - Authorization Code via Browser
After Facebook said "success", I copied the full URI including "http://www." and also without it then I clicked "Paste & Authorize" but it's not able to paste the authorization code. I tried pasting the URI in my text editor, and it works, I can see the URI.
2nd problem - when using Internal
the (your)browser form froze and I have to soft reset to close the "Authorise Access" and "Facebook Tab Settings" forms.
2nd problem - internal authorisation uses the compact .net browser control which in later versions of WM has become very buggy (MS messed it up). Some login pages work better than others, but it isn't very good (hence why I had to use the external method as an option).
Another thing you can try is to ensure you've logged into facebook on the device through the webpage and also clearing the app from your facebook settings if it is in there (which will hopefully allow to you start new).