Yeas, what about it? Oh right, it might stop working after Firefox 57: https://github.com/piroor/treestyletab/issues/1224 . There are people working on it but that isn't true for many other extensions that are no longer under active development.
What is the point of using Chrome if you can't have something like Tree Style Tabs? Unless you're a beta user I don't see the point. I personally will stop using newer versions of Firefox if they stop supporting tabs on the side.