New version of the Firebug Net Panel History Overlay is available. This version requires Firebug version 1.2.0b4; that's the latest version at the moment. The previous version of the history add-on was making Firebug to hang; some functions from Firebug that I used changed as well as some of the NetMonitor and NetPanel behaviours so it was causing hang.
Due to behaviour changes it might happen that with new versions of the Firebug I will have to tweak history add-on but will keep close eye on Firebug changes and if required will update the add-on.