For Windows, as of Win7, Microsoft explicitly recommends *against* doing this:
"In this example from Windows Vista, Outlook and Windows Live™ Messenger are single-instance applications that minimize to notification area icons. ... Note: This icon pattern is no longer recommended for Windows 7. Use regular taskbar buttons instead if your program has desktop presence." [1]
Granted, Thunderbird currently doesn't have a lot of support for Windows 7 features (mostly because Gecko 1.9.1 doesn't support them either), but I think it would make more sense to put effort into Windows 7 support these days.
For Windows, as of Win7, Microsoft explicitly recommends *against* doing this:
"In this example from Windows Vista, Outlook and Windows Live™ Messenger are single-instance applications that minimize to notification area icons. ... Note: This icon pattern is no longer recommended for Windows 7. Use regular taskbar buttons instead if your program has desktop presence." [1]
Granted, Thunderbird currently doesn't have a lot of support for Windows 7 features (mostly because Gecko 1.9.1 doesn't support them either), but I think it would make more sense to put effort into Windows 7 support these days.
[1] http:// msdn.microsoft. com/en- us/library/ aa511448. aspx