For what it's worth, while I can't be specific due to the way I handled the problem, my issues very definitely turned out to be the fault of the browser (IE 11 on Win 7 64 bit). I originally blamed the site (see my previous message) because the issues were almost completely site specific. However, I'd had trouble with some other random sites and had heard a lot of negative comments on IE 11's flakes, so I ripped IE 11 out by the roots and took the browser all the way back to its original, embedded, IE 8. Then I put IE 11 back in clean from scratch using a downloaded installer, not Win Update, and applied all the necessary performance and security updates to present. Presto! Problems solved. The Rendo site now performs flawlessly for me, including product downloads. It remains to be seen what happens with those random other sites, but the indications are pretty convincing.