cd7c41b5_ebug_Preferences___FirebugWiki__Description
[Option] net.hiddenColumns [Valid Values] netHrefCol, netTimeCol, netSizeCol, netDomainCol, netStatusCol [Default] "" [UI Equivalents] Net Panel->Request List header context menu->Columns [Description] 
Hidden columns inside the Net Panel
Firebug Preferences - FirebugWiki