Thunderbird: Hide Header Pane and Buttons in Message Pane

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:

1. In Config Editor, set toolkit.legacyUserProfileCustomizations.stylesheets to true

2. Help → Troubleshooting Information → open Profile Folder

3. In the profile folder, open or create "chrome" directory

4. Edit or create "userChrome.css" inside of "chrome", adding this line:
   .main-header-area {display:none !important;}

5. 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;
      }