What is working correctly: 1) When new mail arrives, the X-notifier icon counter correctly displays the number of new messages; 2) When moving over the icon, the accounts with new mail including the numbers of new messages are correctly displayed.
What is going wrong: Rightclicking the icon shows the roll-down menu with all accounts, the ones with new messages in bold, but the number of new messages in the accounts is missing.
I do not see this behaviour when running under Windows (WinXP, Win7)
Firefox for Linux does not
Firefox for Linux does not have the feature to display number on the right side of menu item.