1817675 - ShadowRoot.adoptedStylesheets returns an opaque object in content scripts

Status: NEW

(WebExtensions :: General, defect, P3)

Description

[Gildas Lormeau]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/111.0

Steps to reproduce:

This issue can be reproduced with SingleFile:

1. Install SingleFile from here: https://addons.mozilla.org/en-US/firefox/addon/single-file/
2. Save with SingleFile this page: https://www.virustotal.com/gui/file/49184a08df66331b671fbe93b40c34afe3b943475bca0568a22bebd1208e1164/details
3. Open the saved page

Actual results:

The layout of the page is broken.

Expected results:

The layout of the page should be OK. Also, this bug does not happen if you do the same test in a Chromium-based browser.

The bug is due to the fact that ShadowRoot.adoptedStyleSheets can't be read in a content script and throws an exception.

Comment 1

[nicoleta.sibisan]

[Tracking Requested - why for this release]:

Hello,

following the indicated steps, I have reproduced the issue on
MacOS 12.5 and Win 11, with Fx versions: Nightly 112.0a1 (21-Feb-2023) and 101.0b1-candidates.

This seems to be a regression:

• last good release: 100.0
• first bad release: 101.0

I used these in mozregression and found:
pushlog_url: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=23768574eb6d1c1191228316adbc082aaf3a7fd5&tochange=6d8eefa220596a138aceee2b8e93529128c98451

Comment 2

[nicoleta.sibisan]

Attachment: add-on_single-file_2023-02-21

Comment 3

[Gildas Lormeau]

Any news about this regression? I'm still surprised that if I use Element#openOrClosedShadowRoot then ShadowRoot.adoptedStyleSheets can be opaque. This is also a compatibility issue since this bug does not exist in Chromium-based browsers.

Comment 4

[Gildas Lormeau]

For the record, I've implemented a workaround for this bug in SingleFile. It consists in injecting a script into the web page in order to read the adoptedStylesheets property and communicate the serialized content to the content script of the extension.

Comment 5

[tophf]

This is not a regression, this was never implemented correctly (the range you found shows the initial implementation of constructable stylesheets), which is an architectural problem in Firefox's XRays. As a workaround you can use document.wrappedJSObject.adoptedStyleSheets directly from the content script without injecting anything. It's still unsafe, of course, and in some cases may require using cloneInto helper function.

Comment 6

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:zombie, could you have a look please?

For more information, please visit BugBot documentation.