Not really memory hogging / memory leak, but FF & Thunderbird started taking more then 5 seconds to shut down. For a while I thought it was a memory leak. I finally installed ZoneAlarm and discovered that Macrovision was the culprit. It somehow got into my system and seemed to be phoning home. I set ZoneAlarm to deny Internet access for Macrovision and FF and TB became like the "olden days".