$$

From FirebugWiki

This command returns an array of HTML or XML elements that match the given CSS selector. This means it is actually a shortcut for document.querySelectorAll().

Parameters

selector

Selector used to match the elements to return. This follows the syntax of document.querySelectorAll(). (required)

Examples

$$(".someClass")

This returns all elements having the class someClass assigned.

$$(".someClass > span")

This returns all <span>s being direct children of elements having the class someClass assigned.

$$("input[type=checkbox]")

This returns all checkboxes.