User Agent: Mozilla/5.0 (Windows NT 5.1; rv:6.0) Gecko/20100101 Firefox/6.0 Build ID: 20110811165603 Steps to reproduce: Go to History -> Show All History -> Older than 6 months. Sort by Location. Select a large number of items (about 50k) which in this case were all with the same hostname. Hit delete. Actual results: Firefox hangs chewing CPU for several hours until I killed it. The whole app hangs, not just the history dialogue box. After I killed Firefox, it hanged again when I restarted it. However, starting a clean session worked. Since that involves losing the open tags, this could be considered a data loss bug. Expected results: Deleting the history could happen faster. Alternatively, a progress bar and cancel button should be shown. The whole app should not hang while doing this operation. It should be possible to delete old items from the history at the same time as browsing.