Thunderbird doesn't show the unread counter on its symbol in the dock for me on Ubuntu 18.04 and 18.10 (both with gnome). Is that normal? If not, does anybody know what the problem could be?
Somehow it worked after a new install of Ubuntu 18.04 and it would have probably if I have not changed something.
There is a discussion around this topic on Mozilla Bugzilla, please leave your comments.
Make sure following is in place to get the new email/message badge/counter for the Thunderbird Icon (Ubuntu Dock, Dash-To-Dock):
1. Ensure that indicator support is installed on your system (packages libindicator7 and libindicator3-7 as mentioned here), it is most likely already installed. This will enable your system to receive indicator messages.
$ sudo apt-get install libindicator7 libindicator3-7
In Thunderbird open Tools → Add-ons: Ensure that the add-on/extension named "Messaging Menu and Unity Launcher Integration" is enabled (it should be installed by default - I disabled as I thought Ubuntu 18.04 has no Unity anymore but Gnome but it also works with Gnome).
Finally restart Thunderbird and maybe logout/in as well.