webext-compactheader - 3.0.0~beta5-2~deb10u1 main

compactheader adds a button to compact Thunderbird’s header pane to a single
line or expand it again. A customization dialog can be opened for the toolbar
in the header pane (right mouse button context menu) to change the displayed
buttons and their style.
.
The shortcut "SHIFT+h" can be used to toggle between expanded and compact
header view.
.
This add-on integrates the functionality of "RSS Linkify Subject"
by Alex Dedul.
https://addons.mozilla.org/thunderbird/addon/rss-linkify-subject/