Well, you almost got it right.
We use proxy analyzing software (like Charon which is totally free and is still the best) against a very reliable proxyjudge to eliminate all the crap, i.e. dead, transparent, Planetlab/CoDeen, so-called "dangerous" and otherwise non-working proxies from the various lists we obtain.
Common sense should tell you that attempting to do this from scratch in your browser would take forever, and of course once you found a proxy you could in fact use it would probably die shortly and the process would have to begin all over. Your understand of the results when testing proxies using proxy analyzing software is incorrect ... providing a reliable proxyjudge is being used.
As the reason should have been abundantly apparent clear, but wasn't ... I asked, "which proxies" you used in order to determine if you even had the necessary knowledge to recognize which ones wouldn't and couldn't work on a particular site (like the one you mentioned). I was looking for a specific list of the ones you used, dead or alive. Get it now?
By the way, if I also haven't made it clear, for the most part, the proxies on this site are no different than those posted to every proxy forum site.