Have you tried out TreeStyle Tabs? It has all of the stacking features I saw in that video, but doesn't have the preview features (maybe you can use it alongside another extension that provides that).
I was about to suggest this too. It's like a more general version of stacking, since you have multiple levels, and much more automatic (but you can drag the tabs into a different tree structure if you want).
I think it would solve the GP comment's problem better too. There's not so much need to use multiple windows if you can just use multiple trees in the same window.
As a bonus there are many plugins for the plugin (!) such as one that lets you use the mouse wheel on it to switch tabs. [1] This is more useful in the tab tree than the normal tab strip, especially since it skips over tabs hidden in collapsed subtrees.
All that stuff about browser engine competition is great but TST is the real reason to use Firefox rather than Chrome.
> I think it would solve the GP comment's problem better too. There's not so much need to use multiple windows if you can just use multiple trees in the same window.
Even if you do want a new window - drag the common parent tab to a new window and it takes its children along for the ride.
I've been using TreeStyle tabs for a few months now.
While I love the tool, it definitely has some rough edges with integration.
It has the same problem Firefox Multi-Account Containers has: Trying to change internal UI for an internal feature by using an addon simply isn't practical (yet).
It was practical before they killed XUL extensions and went with a crippled Chrome clone that can't hide it's horizontal tab bar. It's time for Mozilla to embrace and extend that garbage.
I think it would solve the GP comment's problem better too. There's not so much need to use multiple windows if you can just use multiple trees in the same window.
As a bonus there are many plugins for the plugin (!) such as one that lets you use the mouse wheel on it to switch tabs. [1] This is more useful in the tab tree than the normal tab strip, especially since it skips over tabs hidden in collapsed subtrees.
All that stuff about browser engine competition is great but TST is the real reason to use Firefox rather than Chrome.
[1] https://addons.mozilla.org/en-GB/firefox/addon/tree-style-ta...