It doesn't switch between the tabs but instead closes and reopens the tabs. Every tab on the group is reloaded. You can use https://addons.mozilla.org/firefox/addon/experimental-simple-tab-groups/ from the same developer for proper tab hide/show but its experimental.
Thanks for your review! Please, update Firefox to latest version v61 and after that update addon to STG v3.0 (not experimental). In this version I implement hide tabs api, switch between groups and not close tabs
