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.)
Unlike previous versions of firebug, if you have it closed and don’t have it set to “On for all web pages” it’s actually not running. It’s only on when you open up the panel and are actively using it.
The solution: just open it on the domains you want to use it on. It does a pretty good job of remembering (at least for me).