As Firefox 139 introduces tabGroups API, extensions can now identify and interact with tabs which are part of groups, as well as update tab groups. Initial idea would be to discard all tabs within a group through the context menu. Beyond that, moving discarded tabs to a specific tab group, having a color defined specifically for discarded tab groups. Lots of options. I'd actually invite others to chime in with ideas related to tab groups in relation to this extension.