If you have too much adblock, as I do, you can never visit quora.com. The security check will just loop infinitely.
Funny. Just tested that because I'm always told: too complicated, nothing will work!
And got no check at all.
Edit: Maybe it depends on where you come from, or what they think you come from. Or using VPN. Wrong browser with insufficient base for uBo. uBo configured wrong. (Not?) using an ad-blocking DNS-Server, so that shit doesn't even make it to your local uBo?
Tested from Hamburg, Germany via private tunnel from my home in Colorado, which also works.
Maybe the times are changing. Went through with Adblock and vpn. No looping.