https://addons.mozilla.org/en-US/firefox/addon/sidebery/
This is nice because you can take all your tabs for a research project, condense them to a group and then nap them until you come back to the project.
Oh yes I forgot TST doesn't have that since I haven't used it in so long. Keeping groups of unloaded tabs might not be healthy for me, enables my tab hoarding habit.
https://addons.mozilla.org/en-US/firefox/addon/sidebery/