I usually keep Thunderbird open when my computer is open. But Thunderbird is minimized to the taskbar. It will be more convenient if it is minimized or closed to the system tray as an icon.It will be better if it can display the number of unread messages. Mozilla’s software’s addon system give the method to add more feature to the software by only installing some addons to it. The addons for minimized the windows to system tray are different on Windows and Linux.
My favourite addon for minimizing to tray is FireTray. It works perfect under thunderbird. But it can also be added to firefox, sunbird, seamonkey 2 and songbird. It allows to set up custom icon, minimizing to tray instead of closing and display the number of unread messages. A screen shot on my laptop:
The addon for Thunderbird on Windows is MinimizeToTray. MinimizeToTray can allow to always minimize to the tray instead of to the taskbar, minimize to tray on close and require a double click to restore from the tray.
These addons can also be used on Firefox. But usally I don’t like to make Firefox minimized to system tray. I will use Firefox for more time than Thunderbird, so Firefox should be ready there most of time ;)