So I have a ton of windows open--I just counted, and I have 95 windows open--and I'd certainly agree I'd love to have fewer windows open ;P. But like, each of these windows has a number of tabs in them, and there is only so much space to see tabs. (In fact, I have so many windows open, it breaks something in how Edge is allocating window handles and so when I reboot I have to do a song and a dance involving killing explorer.exe at the right moment to make them all load correctly. I hate how many windows I have open and would love to have fewer.)
And like, at least I'm using Edge (and so I have vertical tabs)... most people who talk about this feature use Chrome: I just don't see what the workflow is you are talking about where you are horizontally scrolling through a ton of tab groups at the top of your window without going insane.
Like, what actually is a concrete example? You said you have a tab group for breaks... how do you even get to that tab group if you have more than like two total tab groups and maybe like three tabs per group? What are you doing to make that workflow actually happen? When you want to enter your break, are you just remembering that your break's tabs are like three or four screens worth of tabs to the right of the tabs for the issue you are working on, and you start scrolling right?
(comment edited a bit later to add this paragraph) I haven't yet found a video of how this looks or works in Chrome but I'm realizing you can maybe shrink them down to the name? I am then wondering what the workflow is for how you choose which tab groups to put into a single window and whether you do keep them all collapsed and are constantly flipping between collapsed tab groups.
For my windows workflow, I am on Windows 10 (and refuse to downgrade to Windows 11) so I can see all of my windows--each of which has a short name I assigned it--on one of the task bars on one of my monitors. I can thereby find the window/groups easily and in each window I have the tabs (using Edge, so laid out vertically, but this would work the same and be just as reasonable with Chrome's horizontal layout) for that group. I can flip between windows with key bindings from the desktop and flip between tabs with key bindings from the browser.
In your example, you discussed having "17 topics" and "500+ tabs"; that's 30+ tabs per topic... I don't see how you are even going to put TWO tab groups in a single window, much less all 17! The Chrome user with their beloved tab groups... how are they handling this? All of the video examples I can find have like three tab groups and two tabs per group and it is already looking impossible to navigate crammed into the horizontal tab strip as the names of the groups are using up valuable real estate for the tabs themselves.
...That said, you say you are using TreeStyleTabs? That's really not "tab groups". I mean, I definitely understand the use case and workflow for TreeStyleTabs as you have a tree-view tab explorer (or at least did when I last used this kind of thing forever and a half ago). I would love a native version of that in a good browser. But that isn't what all of these people in the linked thread saying Firefox should just implement the thing Chrome has are trying to get, as that isn't what Chrome has ;P. "Firefox should land tree-style tabs (or even vertical tabs, for crying out loud, lol)" I 100% grok.