User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:54.0) Gecko/20100101 Firefox/54.0 Build ID: 20170402004002 Steps to reproduce: Extensions that bear the functionality of tab groups, originally introduced by Panorama, are currently not supported under WebExtensions. The core functionality of tab groups is for the user to create groups of active tabs which can be hidden(not present in the tab-bar) and the ability to swap out those groups in a window. I've seen it suggested before that if windows could be hidden, that that could function as tab groups. The Window API could be extended to allow for windows to have a hidden state and for windows to be seamlessly replaced with one another. But I think a more specific API would allow for more flexibility, like having multiple groups unhidden in one window or having one tab belong to multiple groups.

Kris Maglione [:kmag], Bug 1232178 seems to be more about supporting the entire "Tab Groups" extension. I made this bug focus on the actual functionality that are tab groups. But if you insist, can bug 1232178 be reopened. The bug was closed waiting on Luís Miguel [:quicksaver] to do a report(but not in the bug report itself). This was 11 months ago and he stopped extension development. So the bug seems to be just waiting on nothing. I would still suggest rather reopening this bug though.

I believe (reopened) https://bugzilla.mozilla.org/show_bug.cgi?id=1232178#c8 is a good start to track and discuss about all necessary APIs for bring Tab Group into 57.