nsIMicrosummaryObserver in Firefox 3.0

 Called when an observed microsummary updates its content.
 Since an observer might watch multiple microsummaries at the same time,
 the microsummary whose content has been updated gets passed
 to this handler.
 XXX Should this be onContentUpdated?

 @param microsummary
        the microsummary whose content has just been updated

 Called when an element is appended to a microsummary set.
 XXX Should this be in a separate nsICollectionObserver interface?

 @param microsummary
        the microsummary that has just been appended to the set

 Called when an observed microsummary encounters an error during an update.
 
 @param microsummary
        the microsumary which could not be updated