You're probably right, if firefox is searching for IPv6 DNS entries it will slow things down if they can't be found.
I'm just wondering what will happen when IPv6 DNS servers are the norm, will you forget which entry needs changing back.
OnePlus 5T review: Hands-on
Illustrator Andrés Lozano on his improv line work, brazen use of colours & hand sketching
iPhone X review
Comment envoyer gratuitement des gros fichiers ?