It's certainly not worth the risk of getting banned, of course.
Perhaps an alternative to the notification could be changing the color of the extension's toolbar icon to green, to signify the current session has indeed been saved? Or just flashing the icon from blue to green and back a few times. Another idea would be only reinstating the "Save current session" item in the extension's menu (right-click on extension's toolbar icon) with a timestamp of the last saved session underneath.
The notification was nice, but all that is really needed is a confirmation the save was successful.
Thanks for your continued efforts!