Modify the default conversation style to apply the CSS rule 'white-space: pre-wrap;' only on the text of inserted messages. Fix the default margins of smileys.

im/base/content/instantbird/imSmileys.jsm

@@ -141,7 +141,7 @@ function getRegexp(aIconsHash)
 // unused. May be useful later to process a string instead of an HTML node
 function smileString(aString)
 {
-  const smileFormat = '<img src="smile://$1" alt="$1" title="$1"/>';
+  const smileFormat = '<img class="ib-img-smile" src="smile://$1" alt="$1" title="$1"/>';
   return aString.replace(getRegexp(), smileFormat);
 }
 
@@ -167,6 +167,7 @@ function smileNode(aNode)
         elt.setAttribute("src", "smile://" + smile);
         elt.setAttribute("title", smile);
         elt.setAttribute("alt", smile);
+        elt.setAttribute("class", "ib-img-smile");
         smileNode.parentNode.replaceChild(elt, smileNode);
         exp.lastIndex = 0;
       }

im/base/content/instantbird/imThemes.jsm

@@ -213,7 +213,7 @@ const headerFooterReplacements = {
 };
 
 const statusMessageReplacements = {
-  message: function(aMsg) aMsg.message,
+  message: function(aMsg) "<span class=\"ib-msg-txt\">" + aMsg.message + "</span>",
   time: function(aMsg, aFormat) aMsg.time,
   shortTime: function(aMsg, aFormat) "FIXME",
   messageClasses: function(aMsg) {

im/themes/winstripe/instantbird/conv.css

@@ -35,12 +35,17 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
-* {
+.ib-msg-txt {
   white-space: pre-wrap;
   word-wrap: break-word;
 }
 
-*:-moz-any-link img {
+.ib-img-smile {
+  margin-bottom: -3px;
+}
+
+*:-moz-any-link .ib-img-smile {
   border: none;
   border-bottom: solid 1px;
+  margin-bottom: -2px;
 }