When openning several pages (wether pages or tabs) when using Safari I get the following message: Safari can’t find the server. Safari can’t open the page “http://www.facebook.com/” because it can’t find the server “www.facebook.com Firefox doesn't have that problem
*** Bug 15859 has been marked as a duplicate of this bug. ***
I also get this behavior on the release version of Safari on Leopard. Note this is a regression from Tiger, though I'm not sure that it is a WebKit problem, and may be a system problem. I also filed a radar bug on this issue radar://5575622 a few days ago, where there is more info.
According to the info in Radar, this is not a WebKit issue. As such, it will not help to track it in WebKit's bug database.