As of 2/17/09, Knovel has "developed and implemented a patch. We have tested this solution extensively, verified it with individual customers and believe that it resolves the issue." So things should be back to normal, but if you have any problems, please contact us.
An alert for Knovel users:
[Knovel] recently discovered a conflict that occurs with the combination of Firefox 2 or 3 and the new Adobe Reader (version 9) web browser plug-in when downloading Knovel PDF’s. This conflict will interfere with users ability to view PDF documents. While we have determined that the problem does not occur with Internet Explorer 6 or 7, or with Adobe Reader 8, we have yet to identify a fix. We are treating this as an urgent matter and are working with Adobe to find a solution. We will provide updates as we learn more.So, if you are unable to download a PDF using Firefox and the new Adobe Reader 9, you can try using Internet Explorer (or another alternate browser). Hopefully, this will be fixed soon.