When the Thunderbird Message Pane is enabled (View → Layout → Message Pane), the Header Pane and Buttons (Reply, Forward, Delete, etc.) take up an inordinate amount of space; here's how to hide them:
In Config Editor, set toolkit.legacyUserProfileCustomizations.stylesheets to true
Help → Troubleshooting Information → open Profile Folder
In the profile folder, open or create "chrome" directory
Edit or create "userChrome.css" inside of "chrome", adding this line:.main-header-area {display:none !important;}
Restart Thunderbird
On a related note, alternating row colors in the Message List pane can be enabled by adding the following to userChrome.css:
table[is="tree-view-table"] tr:nth-child(even):not(.selected):not(tr:hover) {
-moz-appearance: none !important;
background-color: rgb(240,240,240) !important;
}
/misc | Mar 02, 2024