I get a heck of a lot more bugs (almost 2x) with Firebug on FF4 than with Chrome's inspector, though that still means I have to restart both almost a dozen times (no, really, that many) per day while building a web page.

A recent one: an input field would be spontaneously filled with a "1" if (and only if) Firebug was active. Persisted across application re-starts, but not through a reboot.