That is not true. I am sure add-ons can access the same stuff that built-in tools can. Most of the stuff are exposed as JS objects and there are APIs for a lot

That is not true. I am sure add-ons can access the same stuff that built-in tools can. Most of the stuff are exposed as JS objects and there are APIs for a lot of stuff. APIs for devtools may be a bit hard to find the documentation sometimes. I guess it is because it is still being developed. https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/... Firebug 3.0 will be built on top of the native developer tools https://getfirebug.com/wiki/index.php/Firebug.next https://getfirebug.com/wiki/index.php/Firebug.next