Accessing to DOM functions from Firefox extension

Question

There is a need to access to DOM functions from Firefox extension.

I have code that works perfectly from Firefox console:

var chk = document.querySelectorAll( 'input[type=checkbox]' );
for (var i=0; i < chk.length; i++)
{
    if (!(chk[i].disabled))
    {
        chk[i].checked = true;
    }
}

I want to make a simple extension for Firefox in order to don't copy-paste this code each time. But I've faced with issue that cannot access to DOM functions from main.js.

Could you please advise a way to solve this issue?

Note:

Found this solution but it didn't help:

var wuntils = require('sdk/window/utils');
var window = wuntils.getMostRecentBrowserWindow();
var document = window.document;

Answer 1

main.js will be run only once, and not for each window or tab.

Either use a PageMod content-script or attach a content script via tabs.attach.

The content script would be your querySelectorAll snippet, of course.