[reubenmorais]

No library, at least in Firefox it's defined by devtools and only works in the console (provided the page doesn't have it's own $ and $$ globals).

[0] http://dxr.mozilla.org/mozilla-central/source/toolkit/devtoo...

[1] http://dxr.mozilla.org/mozilla-central/source/toolkit/devtoo...

Edit: It works in the WebKit devtools too:

[0] https://mxr.mozilla.org/chromium/source/src/third_party/WebK...