Add new `runtime.MessageSender` `windowId property

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@xeenon is already working on this.

Since Nov 12, 2026.

Assessment

Difficulty
1/5
Estimated time
1-3 hours
Newbie friendliness
82/100
Issue type
Documentation
Clarity
Clearly specified
Activity status
Active
Tech stack
javascript
Domain
documentation

Research direction

Find the MDN page for runtime.MessageSender under the WebExtensions API reference and read its Type section. Add windowId to the returned properties using the W3C issue linked in the report as context. Done when the Type section lists the property accurately; the issue does not name a test or source file.

Written by the indexing model from the issue text.

Description

Content:WebExt needs triage
MDN URL

https://developer.mozilla.org/docs/Mozilla/Add-ons/WebExtensions/API/runtime/MessageSender

What specific section or headline is this issue about?

Type

What information was incorrect, unhelpful, or incomplete?

Browsers recently added support for the windowId property in runtime.MessageSender.

What did you expect to see?

For the windowId to be listed as one of the returned properties.

Do you have any supporting links, references, or citations?

See W3C issue:
https://github.com/w3c/webextensions/issues/1077

Do you have anything more you want to share?

This has since been implemented in Firefox, Safari and Orion.

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