Error: Permission denied to access property 'handler'

I have a greasemonkey script for Firefox, which yesterday was working perfectly. I tried using it today (no code was modified) and I noticed that it stopped working. Upon further inspection, the script is now throwing the following error:

Error: Permission denied to access property 'handler'

This error is being thrown in the following block of code:

$('body').click(function() {
    // code here
});

This error magically started happening today when the script was working just fine yesterday. I'm not understanding why this error is happening when just trying to do something so basic such as adding an event handler in jQuery.

My script uses jQuery which is already being used in the page the script executes on, so I used this code to make it accessible to GM:

var $ = unsafeWindow.jQuery;

For reference if need be, here are the following Greasemonkey functions I use in my script:

// @grant       GM_getResourceText
// @grant       GM_addStyle
// @grant       GM_xmlhttpRequest
// @grant       GM_getResourceURL

I have tried researching this error and I can't find any answer. All of the questions that look like they might be helpful involve iframes and there is not a single iframe to be found in my code or the website it's run on. I've also tried deleting and re-installing the script and that didn't fix the problem.

Solution 1:

Greasemonkey 2.0 has just been pushed to all Firefox browsers set to auto-update. (GM 2 was released on June 17, 2014, but it can take a few weeks to get through the review process.)

Greasemonkey 2.0 radically changed unsafeWindow handling:

Backwards incompatible changes:

• For stability, reliability, and security the privileged sandbox has been updated to match the new changes to unsafeWindow for the Add-on SDK. In order to write values to unsafeWindow you will need to use the new methods cloneInto(), exportFunction(), and/or createObjectIn().
• The @grant none mode is now the default, and grants will no longer be implied when not explicitly provided. See the post Sandbox API Changes in Greasemonkey 2.0 for more detail.

Ordinarily, to spot-access a page function or variable, you could switch to the new methods but, in your case you are using var $ = unsafeWindow.jQuery; -- which was always a bad practice.

jQuery is a special case and cloning it back and forth is going to break things.
@require jQuery instead, EG:

// ==UserScript==
// @name        _YOUR_SCRIPT_NAME
// @include     http://YOUR_SERVER.COM/YOUR_PATH/*
// @require     http://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js
// @grant       GM_getResourceText
// @grant       GM_addStyle
// @grant       GM_xmlhttpRequest
// @grant       GM_getResourceURL
// ==/UserScript==
...