I don't use it, but Edge has built in vertical tabs fwiw (I know, that's not tree-style).

Firefox haven't actually done anything in particular to help the various TST addon developers though, have they?

My understanding is that when the firefox 57 was released (I believe that was the version that dropped the old XUL add-on model) they did do some work to allow the add-on developer to port it to the new model.

Why exactly they still haven't implemented an easy way to hide the redundant top tab bar I can't explain though!

> I don't use it, but Edge has built in vertical tabs fwiw (I know, that's not tree-style).

I've tried Edge's vertical tabs and it's ok but it's a weak implementation of the idea. It only supports a flat list, and I think new tabs also open at the bottom, not even next to the current tab. TST is vastly superior.

Vertical tabs don't really have anything to do with tree-style tabs except a superficial similarity. The entire point is the automatic hierarchical organization.

I think tree-style tabs can be quite useful to those that care to utilize them, but I think the vertical nature is the much better selling point for most people, since its advantages are very easy to grok. I would like to see better integration of addons like it into firefox so it doesn't feel so hacky, though. It would also be nice to be able to toggle between horizontal tabs and vertical ones like in Edge, rather than having to edit css files to get rid of them like you have to in Firefox.

tst > vertical > horizontal for me, YMMV.

Brave's "skeevy" business model at least is trying innovative ways to get revenue. Firefox on the other hand get's 90% of its funding from Google, which to me generates a clear conflict of interests.

Their business model is selling ads to advertisers for real money, and paid services to users for real money.