I use Edge on my work computer since I can log into it with enterprise SSO and store my passwords and bookmarks to my work account. Not ideal, but I don't do anything personal on my work computer because I already have zero expectation of privacy on it anyway.
Vertical Tabs are an absolute game-changer, especially combined with tab groups. I can actually juggle hundreds of tabs in a single browser window without issue. It's the only thing I can say that Edge got right.
I've been waiting for this development for a long time. I can't wait to have this functionality on my personal computer, on a privacy-respecting FOSS browser no less. The extensions currently available for this are just not that great, it has to be a native feature.
Not the person you replied to, but I can help with an example:
I have the browser reopen the tabs I had open last time, but keeps unloaded until I click on them.
The tabs are in a tree hierarchy, meaning I can collapse an entire group while keeping them all open.
My work involves juggling up to 50 different accounts each for a hand full of websites, so containers allow me to quickly swap between accounts signed into the same page.
Personally, I can't use bookmarks because if they're out of sight, they get forgotten. Keeping things in an open tab is like having the browser constantly bugging me to remind me that I have to do this thing. It doesn't guarantee that it gets addressed in a timely manner, but with the alternative it's guaranteed to not be done at all.
It also helps to keep my place in my work. There's things that I'll always have open because I need quick access to them and don't want the friction of trying to find the page to lead to procrastination. Same with anything that's relevant to work in progress.
When you're keeping things in a tree structure for visual grouping and using containers to manage different logins, bookmarks will lose the tree structure, and you'll have to specify which container to open it in. If your workflow involves a dozen tabs per context, locating the bookmarks and reopening them every time you switch contexts is a significant time and productivity loss.
Consider the classic Evidence Board (also known as string wall, crazy wall, conspiracy board, etc.). Saving everything to bookmarks is the equivalent of putting your board's contents into a drawer, then pinning everything back up whenever you need to look at or update that particular conspiracy. It works, but it's cumbersome, error-prone, and wastes a lot of time; you'd only do this if you only have one board but multiple things to inspect. Leaving tabs open and simply unloading the inactive tab trees is like having multiple separate boards where you just roll them into a closet when you aren't using them.
There are several addons that organize the tabs in the sidebar with a vertical, tree-style layout, with nested tabs that can be collapsed, just like a classic folder structure. This is what GreyBeard was referring to earlier in the thread when he said "The tabs are in a tree hierarchy".
Tree Style Tab has been around since 2007; Sidebery is much newer, and IMO looks and performs better.
You are correct, TreestyleTabs was my jam for years, but I have moved over to Sidebery because it performs better and has better support for containers, as well as being considerably more customizable.
My work involves juggling up to 50 different accounts each for a hand full of websites, so containers allow me to quickly swap between accounts signed into the same page.