Fantastic add-on but it could use a few tweaks.
Group by container there is sort by container but group by container would be a great improvement. Also a way to identify which containers a given tab is. Not sure how best to describe this but i use this feature to manage several clients web consoles like O365, Meraki and Adobe. Since all client use the same console URL this allows me to open the O365 console for serval clients and log into each of them using the client specific ID. When I right click on the firefox in my task bar the Tabs show up but there is no way to differentiate between the various tabs i.e. clients some way of identifing what container the tab is would be helpful.