I have recently acquired a .tk domain and was willing to link it to Firebase hosting as a custom domain.
After reading documentation and following the tutorial, I successfully deployed my first app to Firebase hosting. It is accessible via the default firebaseapp.com url.
However, after trying to set up a custom domain, I have had problems trying to verify my ownership of the domain. I added two TXT DNS records as instructed and have waited for a day for Firebase to verify, but I get the following error:
There was a problem connecting your custom domain. Please contact support.
Thanks in advance.
This was a known problem and has been RESOLVED by the Firebase team.
Michael Bleigh: We're working on a capacity issue with the domain provisioning system.
Tracked on the group discussion "Can't get custom domain to verify"