Firebug 1.4 has an option to enable or disable it for all pages. However, I (usually) only want to temporarily enable it for just one domain. In earlier versions, this was trivial, but I can't find anyway to do it in 1.4.
(To give context, I typically have several windows open with several tabs each. Many of the sites open are ajax heavy (e.g., gmail or Google docs) which don't play nicely w/ Firebug. So if I want to quickly see, say an HTTP response code, for a particular site, I have to enable Firebug for all sites making my browser crawl.)