As reported in https://github.com/webcompat/web-bugs/issues/59078

STR:

1. Open https://www.games-workshop.com/en-WW/Daemon-Prince-2016 in Firefox Nighlty 83.0a1 (2020-09-30)
2. Click on the right arrow to get to the 360 view
3. Click on the 360 icon and try to rotate the image

Expected:
Image rotates

Actual:
Image doesn't rotate

From mozregression:

11:00.62 INFO: Narrowed integration regression window from [600fcb1c, 7d6d00b5] (3 builds) to [600fcb1c, 37ddb997] (2 builds) (~1 steps left)
11:00.62 INFO: No more integration revisions, bisection finished.
11:00.62 INFO: Last good revision: 600fcb1cdee14e03c6823d69e67c2566849b0aac
11:00.62 INFO: First bad revision: 37ddb997bbf6dc6dd6a444dc4f9373de5d8be581
11:00.62 INFO: Pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=600fcb1cdee14e03c6823d69e67c2566849b0aac&tochange=37ddb997bbf6dc6dd6a444dc4f9373de5d8be581

I'm getting an error Uncaught TypeError: F.shift is not a function in this function:

    B.implement(Function, {
      $J_TYPE: 'function',
      jBind: function () {
        var F = w.$A(arguments),
        E = this,
        G = F.shift();
        return function () {
          return E.apply(G || null, F.concat(w.$A(arguments)))
        }
      },

I think this code is a part of this paid library https://www.magictoolbox.com/magic360/ Also 360 viewer examples on their website don't work in Nightly.

Tom would you be able to take a look? We perhaps can contact the library author if needed

Thanks for reporting this issue! This might mean we can't standardize the item method. Seems like this is a problem in the paid Magic 360 JS library.

Looks to me like it's wrongly detecting arrays as HTMCollections now:

jTypeOf: function(E) {
 ....
if (E.length && E.item) {
  return "collection"
}
...
}

Ups bug collision. I first opened a bug on the proposal page: https://github.com/tc39/proposal-item-method/issues/28

Hi Ksenia! Do you think you could reach out to MagicToolbox and ask them if it would be possible to update their code and if they also have some way to get all customers to update as well?

Thanks for looking into this Tom. Yeah, I'll reach out to them.
Update: contacted through the form https://www.magictoolbox.com/contact/

Do we have an idea of the webcompat impact for our users? Could we get this bug prioritized for triaging purposes wrt to our upcoming releases? Thanks

This is Nightly only for now.

The issue in Magic 360 has been addressed by its maintainers. It will probably take time for all their customers to upgrade to the newer version

the problem is now solved

item was renamed to at.

This was fixed by backout for Firefox 83. https://hg.mozilla.org/mozilla-central/rev/b8d82fc2371e020ade6144aa7f5892bf979761bb

Array.prototype.item was also backed out. https://hg.mozilla.org/mozilla-central/rev/8b1680a2b965