Help > Troubleshooting Information
   click on 'Open folder' button 

   Close Thunderbird now - this is important. 

   Create new folder and call it chrome note the spelling - use a lower case 'c' It should be in the same place as the 'Mail' folder. 

   open Notepad
   Copy and paste the below code.  Tweak to suit your needs.
   Save document.

 font-family: Verdana !important;

      background-color: #f0fdfa !important;}

      background-color: Highlight !important;

      background-color: #f0fdfa !important;
      color: #000 !important;}

      background-color: Highlight !important;

I have a custom background color and after updating to Thunderbird 68 the odd line backgrounds became white and so it became stripped... very annoying. It took me a while to figure out how to fix this to a solid background. Here is my solution: In Thunderbird: Help > Troubleshooting Information click on 'Open folder' button a new window opens showing the contents of your Profile folder. Close Thunderbird now - this is important. Create new folder and call it chrome note the spelling - use a lower case 'c' It should be in the same place as the 'Mail' folder. open Notepad Copy and paste the below code. Tweak to suit your needs. Save document. << start below >> /* Global UI font */ * { font-size: 9pt !important; font-family: Verdana !important; } #folderTree {background-color: #f0fdfa !important;} #threadTree {background-color: #f0fdfa !important;} #threadTree treechildren::-moz-tree-row(odd) { background-color: #f0fdfa !important;} #threadTree treechildren::-moz-tree-row(selected, focus) { background-color: Highlight !important; } #folderTree treechildren::-moz-tree-row(odd) { background-color: #f0fdfa !important; color: #000 !important;} #folderTree treechildren::-moz-tree-row(selected, focus) { background-color: Highlight !important; } << end above >>