[Bug] Not working for RSS feeds in Thunderbird

Prerequisites

• I searched for any existing report about this bug to avoid opening a duplicate.
• I can reproduce this bug in a new, unmodified web browser profile with Dark Reader installed as the only extension.
• I understand I need to use the Broken Website Report template if this bug I am reporting occurs on a single website.

Bug Description

I think the problems started when I updated to Thunderbird (TB) 155. Emails are displayed correctly; DR works as expected there. But nothing happens in RSS feed messages. The settings look OK:

This applies to all sites that I read via RSS. These sites are processed correctly by Dark Reader in Firefox. The issue is only in Thunderbird. It has been working for years in TB before.

Website Address

For example https://www.aktuality.sk via Feed URL: https://www.aktuality.sk/rss/

Steps To Reproduce

1. Switch TB to a cards view.
2. Subscribe to any RSS feed, e.g. https://www.aktuality.sk/rss/
3. Click on any message from the feed to display a page.

Expected Behavior

The page in the preview window should be dark.

Actual Behavior

The page in the preview window is not displayed correctly, it's not dark.

Screenshots

No response

Operating System

Window 11

Web Browser name and version

Thunderbird 155.0.1 (64-bit)

Dark Reader version

4.9.131

Additional Context

No response