Digging through the logs, I noticed that the Opera GETs stop after the server issues a 304 (a re-used image requested a second time on the same page). Once the 304 is sent, everything stops. But Firefox never issues a second GET for that graphic....
Ah-Ha! It's my caching preferences that are making the difference, and not the browser itself or the fact of it being asp. The IIS server is just stopping after a 304. Well, I've left the topic area of the Browser forum, and will probably need to haunt the Microsoft forum now.
Thank you encyclo for pushing me to look more seriously at the server logs.
I have confirmed the analysis, by the way, by setting my Opera preferences to "Never" for rechecking images. The page loads fine with that setting. However, I'd better check other browsers and set them to "always check"...it still looks like maybe Opera is stopping after the 304 rather than the server, because no more GETs arrived.
By the way, one cookie is being set, and the server headers are:
User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.6) Gecko/20040206 Firefox/0.8
HTTP/1.x 200 OK
Date: Wed, 01 Sep 2004 12:55:06 GMT
Expires: Tue, 31 Aug 2004 20:15:06 GMT
Set-Cookie: ASPSESSIONIDQCACARRB=BJCEJADDAOMJHGBCBPNCPKCA; path=/