I learned something new today when developing in the Firefox Dev Tools console (although this applies to Chrome too)—something which was really useful and which I thought I’d share.
Basically, type $$('selector') into the console (replacing selector as desired) and it’ll give you back all matching elements on the page.
So for example, $$('script') or $$('li').
Similarly you can select a single element by instead using one dollar sign ($).
These seem to be console shortcuts for document.querySelector() (in the case of $) and document.querySelectorAll() (in the case of $$).
The other really cool thing is that the resultant nodeList is returned as an array, so you could do e.g. $$('li').forEach(…) or similar.
via @rem (Remy Sharp)