I've had this problem for months, but given I didn't have time to test out scenarios only bringing it up now.
Environment: Vista Ultimate 64, running latest build NIS2009 with Firefox 3.0.5 - Only add-ins are NoScript and AdBlock Plus. SafeWeb addon was installed.
On occasion (I'd put it at 1-2 times per hour), Firefox will show as "Not responding" for about 10-20 seconds before going to the page I requested. Processor is not spiked, memory is fine... It just happens. After the occurrence, everything is fine. This happens on all three machines I have NIS installed on.
I first thought it might be SafeWeb, but after re-imaging a machine I still had the issue occur with SafeWeb not installed. I then thought this might be related to Firefox or Vista 64, but I just finished a day of testing with a machine using a different antivirus and the issue has not appeared. With everything else the same, I'm left thinking it has to be my installation of NIS. As I've had it happen on three machines (and various reinstalls), I don't think its an installation issue as much as interaction between NIS, my machine, and Firefox. Firefox is the only app this happens to -- Possibly somethign with the IPS module?
I consider it a minor bug, but wanted to bring it up to see if anyone else has experienced this (and to see if maybe there is a resolution).