Review for Message Header Toolbar Customize by Alexander Ihrig
Rated 5 out of 5 stars
Really perfect re-implementation of this missing/removed feature in Thunderbird 78 using the collapsed="true" attribute. And the best is, that it supports other extensions, which add buttons to the toolbar (like my "Allow HTML Temp" addon).
This review is for a previous version of the add-on (2.0.4).To create your own collections, you must have a Mozilla Add-ons account.