I was looking for a solution for Tab Groups becoming obsolete with Fx57; Tree Tabs is the solution. The vertical tab bar with tab grouping+collapsing allows me to manage different sets of tabs for different projects. I would love for container coloring support; I think that's all it's missing, besides a built-in dark theme.

I'm able to hide the horizontal tab bar via custom chrome css, a la https://github.com/jonathanKingston/sea-containers#demo-as-sidebar-only