You'll need to edit the userChrome.css file in your Thunderbird folder (or create the file if it isn't there). There's quite a good tutorial here: http://www.linnhe2.free-online.co.uk/thunderbird/chrome.html It includes several examples but unfortunately not one to adjust the line height. However the css property line-height: 150% (or whatever percentage you want) should work. You just have to experiment really to get it the way you want. Just about everything in the Thunderbird interface can be tailored this way.

Thanks, amanchesterman, I have created the file "userChrome.css" in ~/Users/Username/Library/Thunderbird/Profiles/chrome/ (I'm on a Mac), and pasted some folder-pane-tweaking code into it it from the page you had suggested. Restarted TBird. No effect at all. Maybe I should have put the file into another directory?

I don't use a Mac so I'm rather out of my depth here. However according to this page it looks as if you haven't got the path right: https://developer.mozilla.org/en-US/docs/Mozilla/Thunderbird/Thunderbird_Configuration_Files The page is somewhat out of date but I guess the path hasn't changed much. If it's still correct, in your /Thunderbird/Profiles/ folder there should be another folder with a name like xxxxxxxx.default where the x's are a random string of 8 characters. That's your actual Thunderbird profile which contains all your mail and settings. The /chrome/ subdirectory needs to be created within that.

amanchesterman said

The /chrome/ subdirectory needs to be created within that.

Thanks, NOW it works.

Figured out, line-height attribute doesn't work in userChrome.css. Like, at all. So I searched the Net and tried this code instead:

/* Row Height*/ treechildren::-moz-tree-row {

   margin-top: 2px !important;
   margin-bottom: 2px !important;

}

Success )