What could stop Array.prototype.filter() from running in greasemonkey script that runs fine in console

Here is the code:

function fil(val) {
  console.log('fil'); // never written to console when run in greasemonkey
  return true;
}
var temp = unsafeWindow.someobject;
console.log(temp); // looks fine
temp.filter(fil); // never happens in greasemonkey

If I run the very same code (without unsafeWindow of course) on the same object in the firebug console it outputs just fine. What could be the reason?

Edit to clarify: when run in greasemonkey the string 'fil' never is written to the console which shows that fil() is never called. Also if I do something like console.log(temp.filter(fil)); I never get to see a result from that in the console when the code runs from greasemonkey. (although I know it should because the line above tells me temp exists and the code runs up to that point.

Solution

In my case, in Firefox 45 and Greasemonkey 3.7, this code works fine:

// ==UserScript==
// @name        Array.prototype.filter() test
// @namespace   http://stackoverflow.com/questions/33675675/
// @include     http://stackoverflow.com/questions/33675675/*
// @version     1.0
// @grant       none
// ==/UserScript==

function fil(val) {
  console.log('fil'); // never written to console when run in greasemonkey
  return true;
}
var temp = unsafeWindow.allowedHosts;
console.log(temp); // looks fine
temp.filter(fil); // never happens in greasemonkey

And outputs:

Array [ "stackoverflow.com", "serverfault.com" ]
fil
fil

But changing none to, for example, GM_getValue in line:

// @grant       none

Outputs only:

Array [ "stackoverflow.com", "serverfault.com" ]

This is because passing to @grant any value other than none enables the sandbox, and from what I can see, the wrapped objects don't support methods that take callback functions as arguments.

You may be able to replace some GM_* privileges with the compatibility layer that you can find in the link above. Then you could disable the sandbox by setting @grant none and you're all set.

However, if you need the original functions, you could use [].filter.call(temp, fil) instead of temp.filter(fil), as mentioned in the comments.