[edmcnulty101]

Could someone write a browser extension to override DNS?

And basically create a new domain system for people with that extension installed?

[icedchai]

Something similar was attempted decades ago and failed, with alternate DNS roots. See AlterNIC for an example: https://en.wikipedia.org/wiki/AlterNIC

[doublerabbit]

And opennic.org

[detaro]

The "usual" way of doing that is by making DNS servers that create their responses based on whatever other name resolution system you want them to do.

[hanniabu]

ENS is the way forward