Rated 5 out of 5 stars

Please remove the mail icon for the subject field.

It should only show an icon if you have replied to a message (not for every message).

Thank you, this will work nicely!

This review is for a previous version of the add-on (3.0b5). 

I'll take 4 stars, thank you :)

As a workaround you can add this to userChrome.css:

/* ..... restore default subject column icons ..... */

treechildren::-moz-tree-image(subjectCol) {
list-style-image: none !important;

treechildren::-moz-tree-image(subjectCol, forwarded) {
list-style-image: url("chrome://messenger/skin/icons/forward.svg") !important;

treechildren::-moz-tree-image(subjectCol, replied) {
list-style-image: url("chrome://messenger/skin/icons/reply.svg") !important;

treechildren::-moz-tree-image(subjectCol, replied, forwarded) {
list-style-image: url("chrome://messenger/skin/icons/reply-forward.svg") !important;

treechildren::-moz-tree-image(subjectCol, new) {
list-style-image: url("chrome://messenger/skin/icons/newmail.svg") !important;

treechildren::-moz-tree-image(subjectCol, imapdeleted) {
list-style-image: url("chrome://messenger/skin/icons/cancel.svg") !important;