Sometimes the plugin either doesn't work as expected, or just doesn't work (file upload specially), so you have to end the application using the task manager on Windows (not user-friendly at all).
It would be useful to have an option for closing or exit the PowerTab, as every other application does.
Thanks for your feedback. The easiest way to close the Powertab is by right-clicking on the "p" in the taskbar and choosing "close". This is also where you find the toggle for autostart of the Powertab and where you easily log in/out. After the Powertab is closed you can restart it from the start menu.