Rated 3 out of 5 stars

There needs to be an internal name set up in install.rdf and chrome.manifest, otherwise it turns into a clone of SeaMonkey Modern when one updates the application. This is what I did in install.rdf to give it one:
<em:internalName>graymodern</em:internalName>
In chrome.manifest, I put the name into each line that begins with "skin"; for example:
skin messenger graymodern chrome/modern/skin/modern/messenger/

This review is for a previous version of the add-on (1.0).  This user has other reviews of this add-on.