Really great to see this extension, but please please allow the user to select whether or not tabs are closed in the current group when switching to a new group. I would even suggest to make it the default to keep all tabs open when switching since the current system of closing tabs will cause more headache, confusion, and mistakes from your users than any benefit like a lower memory footprint would make up for. It takes 5 seconds to close and re-open FF if you're looking to free up resources.