as others have mentioned , I too use zen browser.

But I am keeping a close eye on the Servo browser engine project.

#Servo
#servo_engine

#ZenBrowser

I'm using #zenbrowser as a casual replacement to Firefox atm. The native customization options are a big feature plus for me.
#arkenfox user.js can be applied to any #firefox fork.

In the future #ladybird could be a good option, lets see...