Custom app icon not worked

[varlesh]

extensions.firetray.mail_icon_custom - this icon applied and worked fine.
extensions.firetray.app_icon_custom - this icon NOT applied.

• Ubuntu 18.04 with KDE and Gnome ( use libappindicator)
• Thunderbird 60.6.1
• FireTray 0.6.5
  LOG:

(thunderbird:9372): GLib-GObject-WARNING **: 11:53:01.319: ../../../../gobject/gsignal.c:2523: signal 'activate-event' is invalid for instance '0x7f0693fe3fe0' of type 'AppIndicator'