Firebug Download For Firefox 12 › < Top >

If you're debugging legacy code or testing on an old system, consider running with networking restricted — but for any real development, upgrade to a modern browser.

I notice you're asking about for Firefox 12 — that's a very old version (Firefox 12 was released in April 2012). Firebug has since been discontinued and is no longer maintained. firebug download for firefox 12