HTML shown as attachement on Android

Checklist

• I have used the search function to see if someone else has already submitted the same bug report.
• I will describe the problem with as much detail as possible.

App

Thunderbird for Android

App version

20.0

Where did you get the app from?

Google Play

Android version

16

Device model

oneplus

Steps to reproduce

HTML email that is encoded like

Content-Type: text/html; charset=UTF-8;
	name=attachment-7e164bea-130d-4de5-9739-4684fca12345
Content-Transfer-Encoding: base64
Content-Disposition: inline;
	filename=attachment-7e164bea-130d-4de5-9739-4684fca12345

does not render inline. Instead, it is displayed as an attachment without file extension. This might explain why it is not rendered.

Viewing the attachment in Firefox reveals the text.

The same email displays well on my Thunderbird desktop 140.12.1esr

Expected behavior

Display HTML text inline.

Actual behavior

Not rendered inline. Instead, it is displayed as an attachment without file extension.

Logs

No response

Reproduce the issue in Thunderbird for Android using the supplied MIME headers and trace the message-viewing path that distinguishes inline HTML from attachments. Confirm the message renders HTML inline rather than as an extensionless attachment, and add or update a regression test covering this MIME shape.