OK, re-enabling userChrome.css according to http://forums.mozillazine.org/viewtopic.php?f=30&t=3064381&start=6
and creating a userChrome.css as follows: /* Thunderbird userChrome.css */ @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); #folderTree > treechildren::-moz-tree-image { width: 10px !important; height: 10px !important; } #folderTree > treechildren::-moz-tree-cell-text { padding-bottom: 1px !important; } provides a temporary solution! -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1918249 Title: Icons in folder pane don't scale for hidpi, breaks rendering To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/1918249/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs