I noticed that the Instant Message icon is not displayed using the
Modern theme when initially opened; however, it does display once it is
hovered over and stays displayed afterwards, even if the Addressbook is
closed and then reopened.

This doesn't occur in the Classic theme.

After looking at the two CSS stylesheets it seems that Modern has these
icons separate from the button image map; whereas, Classic has added
them to the button image map.

I have several themes that exhibit the same problem and, as mentioned
above, the common difference is that those themes that have the Instant
Message icon separated from the button icon map fail and those that have
it included don't.

Is anyone else experiencing this problem?

Mozilla Tips: http://www.ufaq.org/ , http://ilias.ca/
About Mozilla: http://www.mozilla.com/
Mozilla Themes: http://www.projectit.com/freestuff.html