First of all, my Mac runs OS X 10.9.1, in case it bears any significance.
I used to find free proxies on proxy-list.org, and most of the proxies I tried worked fine for me. However, for the past two months or so (maybe only after upgrading to 10.9 Mavericks, I'm not sure), things broke. None of the proxies listed on proxy-list.org ever worked any more. (Whenever I configure a proxy for HTTP and HTTPS, and try to load a web page, Chrome always returns a "connection to ... interrupted" error.) However, those proxies are obviously working proxies themselves, according to multiple proxy checkers.
Therefore, I'm wondering what's wrong on my part. I don't think there's any problem with my configurations—otherwise I shouldn't have succeeded in the past. Any ideas? Thanks.