I work a lot on a Firefox extension, and honestly, the absence of dev tools for addons is really painful. Developping our extension for Chrome was super easy, since all their default devtools work in extension panels as well, but in Firefox it's been a nightmare, almost no tools. We are left off in a console.log madness trying to figure out what's causing bugs.
It would be soooooo awesome to have Firefox's default devtools working easily in extension panels!