I use Privoxy for ad-blocking, and since upgrading to OSX 10.9, Safari seems to fail to connect to the proxy server 10% or 15% of the time, giving me broken images and whatnot. I believe it's not a problem with Privoxy itself -- I've tested that under load. It seems like Safari itself just sometimes decides to throw up a "proxy not responding" error before even attempting to connect to the proxy server. Not a timeout, it's fast.
I'm open to switching to a different ad blocker, but "Adblock Plus" doesn't exist for Safari, and the other one, confusingly and possibly sleazily called just "Adblock", doesn't block Youtube video ads, so that's a non-starter.
No, I don't want to switch to Firefox, Opera or Chrome.
Update: I figured it out! Turns out I hadn't merged the privoxy config file in a while and there were some new entries that needed to be set because the defaults make it fail, particularly, the problem goes away when I am no longer missing the default entry keep-alive-timeout 5.
Not entirely clear why this problem manifested itself with Safari and not Firefox, but this seems to fix it.