Multi-account-containers: window.open in greasemonkey script crashes tabs

[Narcha]

// test this on an empty HTML file
var a = document.createElement("button");
a.innerHTML = "click me"
a.onclick = ()=>{
  window.open("https://example.com");
}

document.getElementsByTagName("body")[0].appendChild(a)

Calling "window.open()" in a Greasemonkey script in a non-default tab container crashes the tab.
It does not crash

• when the JS is not in a Greasemonkey script, but on the page itself

- when executed in the default environment

• Multi-Account Containers Version: 6.2.5
• Operating System + Version: Manjaro Linux (5.6.16-1-MANJARO)
• Firefox Version: 77.0.1
• Other installed Add-ons + Version + Enabled/Disabled-Status:
  DuckDuckGo Privacy Essentials 2020.5.28 true jid1-ZAdIEUB7XOzOJw@jetpack
  Greasemonkey 4.9 true {e4a8a97b-f2ed-450b-b12d-ee082ba24781}
  NoScript 11.0.31 true {73a6fe31-595d-460b-a920-fcc0f8843232}

Actual behavior

Tab crashes when window.open() is called from a Greasemonkey script.

Expected behavior

The tab not crashing.

Steps to reproduce

1. create a new HTML file, add body tags
2. install the given Greasemonkey script, configure it to affect the page
3. click the generated button

Notes

I found #1549 , but I believe this is a different bug.
Still, I am not quite sure if this is a bug with containers or with Greasemonkey.

[hckr]

Still, I am not quite sure if this is a bug with containers or with Greasemonkey

The same issue occurs in normal add-ons, see the issue referenced above.

[hckr]

I found a workaround: using window.wrappedJSObject instead of plain window. It seems to work also in Greasemonkey userscripts.

For example:

window.wrappedJSObject.open("https://mozilla.org");

I'm not necessarily fan of this solution/hack though.

[Narcha]

@hckr thanks for the workaround, it works great.

[hckr]

Unfortunately, I discovered that this workaround causes problems with messaging between windows via postMessage – responding with e.source.postMessage from popup window to the main window (e.source) fails.

So, I guess it solves most issues, but not all.

(It isn't connected to this extension in any way, rather to how window.wrappedJSObject is implemented, I guess.)

[filbo]

It is very likely you would need to use XPCNativeWrapper or something, to re-wrap, at some point in the whole procedure. I'm only speaking from docs, haven't tried any of this myself. https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Sharing_objects_with_page_scripts mentioned XPCNativeWrapper(), but the document it points to for 'much more detail on this', Xray vision, doesn't mention that at all, so who knows. Perhaps you would need Components.utils.waiveXrays(), which _is_ mentioned in that doc.

And by 'at some point in the whole procedure' I mean, I don't have a firm enough grounding to know if you would need to do that in the popup window, main window, both, or what...

And, of course, if you're trying to write an extension which is portable across FF, older FF, Chrome. etc., you're going to be up to your eyeballs in polyfills, browser sniffing, or worse.

[hckr]

@filbo I already use something specific to Firefox. What I need is quite simple – sens message to a window created with window.wrappedJSObject.open, and then in the receiving handler send a response (with is normally possible via e.source.postMessage where e is an event received by onmessage handler). This handler is also created by the add-on, both windows have the same domain loaded inside. It works without wrappedJSObject stuff.

[filbo]

Explore. Does e.wrappedJSObject exist? Then maybe you need to use e.wrappedJSObject.source.postMessage(). Or if it doesn't exist, maybe you need to wrap it with XPCNativeWrapper(). Or maybe this stuff Just Won't Work. The people who wrote / maintain the containers stuff should have a much better mental model of this than someone who's just looking at docs like me...

[hckr]

I explored it a bit and came to a conclusion it won't work. .wrappedJSObject does exist on this event, but messages aren't received by the other end.

I wrote all this just in case someone came by and happened to know the solution.