I really enjoy the Firefox tree view add-on for managing tabs.

Ever since they added tab stacking it's become vital to how I use browsers. Idk if I could switch to something else without it having a way to approximate that flow.

Floorp, a browser based on Firefox, has Workspaces I believe (along a LOT of other stuff). Might be worth checking out.

Their website is in Japanese, but the GitHub page is in English. I’m sleepy and too lazy to link stuff right now, sorry.

Completely agree.

I don't think that's the same thing.

Tab tiling means having two or more tabs open at once, so that both can be worked on at the same time.

Not exactly what you are looking for but Sidebery has a feature called Snapshots that allow you to save a group of tabs in their current state to open them later.

There are tab group manager addons. One of them is Simple Tab Groups

Idk about an extension in firefox but there’s a firefox fork than includes workspaces by default called floorp https://github.com/Floorp-Projects/Floorp/releases/tag/v11.1.0

https://addons.mozilla.org/en-US/firefox/addon/simple-tab-groups/

I'm using this one. You can set hotkeys to switch to a specific named group or to go to next or previous. I use it all the time.

FYI, Vivaldi posted their opposition to WEI here. If website operators use the scheme then browsers not implementing it are at a loss. Hopefully every chrome based project (including edge!) is able to remove it so Chrome official is the only one where it works. Starving the approach of participants sounds like the only easy to make it fail.

Workarounds are generally bad in most software situations. Yes we could tile the windows instead of the tabs, but

• We would have to put them all back in one window when exiting to get them saved
• Alternatively we could use profiles, but that's a hassle on startup.
• It probably eats up more resources
• If we wanted to relocate our "Firefox workplace" to somewhere else (let's say another monitor) we would have to drag multiple windows.
• On linux some window managers are just not there with tiling yet (and they might never be).
• Also it looks bad and is a workaround to something that should just be. Hope I didn't miss anything, and you sir have a nice day :)

Given that part of Vivaldi is closed source, it will always be 'worse' than Firefox in terms of privacy.

That's a very broad question. They have some advantages, like built in ad-blocker (firefox only has tracker blocker) with customizable lists, no analytics except basic user counting.

Firefox in theory has the advantage of being open source though I doubt anyone has independently taken it upon themselves to audit the code base of a whole browser, without payment.

If you need 2+ tab stacks, I think you would rather need a tab group manager, like Simple Tab Groups. It does not support nested groups, but you may be able to imitate it with "folder names" in the group name, or there might be better such addons too.
Honestly, I don't see how 2+ rows of tabs (+stacks) would fit on screen