Prerequisites

• I verified that this is not a filter list issue. Report any issues with filter lists or broken website functionality in the uAssets issue tracker.
• This is NOT a YouTube, Facebook or Twitch report. These sites MUST be reported by clicking their respective links.
• This is not a support issue or a question. For support, questions, or help, visit /r/uBlockOrigin.
• I performed a cursory search of the issue tracker to avoid opening a duplicate issue.
• The issue is not present after disabling uBO in the browser.
• I checked the documentation to understand that the issue I am reporting is not normal behavior.

I tried to reproduce the issue when...

• uBO is the only extension.
• uBO uses default lists and settings.
• using a new, unmodified browser profile.

Description

We need to expand syntax of prevent-xhr, prevent-fetch, trusted-prevent-fetch and trusted-prevent-xhr scriptlet by allowing specifying HTTP status code and modifying an HTTP header for XHR and fetch API.

For example, by executing the following code without adblocking, you can receive 0 as its HTTP status code:

(await fetch('https://www3.doubleclick.net', { method: 'HEAD', mode: 'no-cors', cache: 'no-store' })).status

However, the following none of scriptlet filters work:

example.com##+js(no-fetch-if, doubleclick.net, , '{"statusText": ""}')
example.com##+js(no-fetch-if, doubleclick.net, , '{"type": "opaque"}')
example.com##+js(no-fetch-if, doubleclick.net)

because uBO returns 200.

Also, removing, modifying and adding an HTTP response header & its value is required.

A specific URL where the issue occurs.

https://srank.kr/

Steps to Reproduce

1. Apply each the provided scriptlet filter
2. Visit https://example.com/
3. Execute the provided code.

Expected behavior

Return 0.

Actual behavior

Return 200.

uBO version

1.66.4

Browser name and version

Firefox Dev 144.0b9 flatpak

Operating System and version

Ubuntu 25.10