Used to check all checkboxes in a page.

check_all.js

// Paste into Firebug or Chrome Dev Tools console
// when viewing a page with multiple checkboxes.

(function(d) {
  var input = d.querySelectorAll('input[type="checkbox"]');
  var i = input.length;

  while (i--) {
    input[i].checked = true;
  }
})(this.document);

Simply input[i].checked = true would work as well.

Since this is meant to be used in a web inspector thingy, you could use qSA:

[].forEach.call(document.querySelectorAll('input[type="checkbox"]'), function(el) {
  el.checked = true;
});

If you use the Web Developer add on in Firefox under the Forms section you can use Populate Form Fields. Has the added benefit of populating all empty text-fields too.

I can't get either one of these scripts to work in Firebug Lite or Chrome's Dev Console. I'm actually trying to do the opposite and uncheck all checkboxes on pages that don't have an check/uncheck all. i.e. Facebook's notification page. http://cl.ly/2R2U1m1w392n2S2K0z3S Any ideas?

@kevinSuttle - This is what you need...

(function(d) {
  var input = d.querySelectorAll('input[type="checkbox"]');
  var i = input.length;

  while (i--) {
    input[i].checked = false;
  }    
})(this.document);

ROCK! Thanks Nathan!

Just used this on a shady recruiter. The first snippet works best.

Thanks! @nathansmith