After having recently moved all my mail to Thunderbird from Kmail, I was dismayed to discover that Thunderbird will not "minimize to tray," meaning that I would get no new mail notifications and no "Lightning" calendar reminders without TB being open on the desktop or minimized to the taskbar. A little Googling provided the following answer.
- In Konsole, login as root and type the following: apt-get install alltray
- Find Thunderbird in the KDE menu and RIGHT click on it. Select "Edit Item."
- The KDE Menu Editor will open. In the "Command" field, type the following: alltray -s -l thunderbird %u
- Click the save button on the KDE Menu Editor and close it.
- Start Thunderbird and follow the instructions that Alltray provides.
Thanks to Techthrob for this tip!