Cookie-deletion and blocking fails for this site.
I'm using the current Firefox-ESR for Linux x86_64. Under Settings > Privacy and Security > Cookies and Site Data > Manage Exceptions, I blocked http:174.138.51.92 and https:174.138.51.92 several weeks ago. But Manage Data shows 10 cookies last used 45 minutes ago, and Remove Selection for these cookies fails (incidentally retaining the "last used" value), even when repeated multiple times as fast as I can mouse the select, then Remove Selection, then Save Changes then Manage Data .
How can I delete these cookies and site data? And why does it fail for this site and this site only? And how can I block them permanently, short of black-holing that site in /etc/hosts?