Please clarify, possibly describing what you are attempting to do. thank you

There's an add-on called 'Message Header Toolbar Customize' Allowing the user to remove all or some of the toolbar buttons on the message header. Been using it for some time. Hope that helps.

There is a version that installs in TB 142:

https://hogiblog.blogspot.com/2025/

I keep trying to install the add-on but I get the same results. This nis the link use form your link .

https://hogi.sakura.ne.jp/en/downloadcgi.rhtml?msghdrcust

This is the download link to which sfhowes was referring: https://hogi.sakura.ne.jp/xpi/msghdrcust244_TB128_no_max_ver.xpi

This is the direct download that works here in 142:

https://hogi.sakura.ne.jp/xpi/msghdrcust244_TB128_no_max_ver.xpi

Click the gear icon in the attached picture, install add-on from file...

Got it. Thanks much.