If by "latest version" you mean the 1.2 alpha, which is only accessible from the Firebug website, not addons.mozilla.org. See https://bugzilla.mozilla.org/show_bug.cgi?id=411814#c60

On FF 3 beta 5, Firebug would mercilessly crash my browser any time I made the mistake of trying to expand an email in gmail, or reorder things in my google homepage.