Still trying to get used to it really at the moment, couple of things I've noted...
- Nowhere near as easy to get to the history as in Firefox, no "Recently Closed Tabs" section. This was useful in Firefox
- You can't filter your history by text in the address bar. For example, if I'd watched "See you again" in youtube, I can't search for it easily like in Firefox.
- Feels a bit slow opening new tabs as a link from a page (scroll click), and they open at the very end of the tab list, I'd prefer if they opened immediately after the tab I'm on.
But it's only a technical preview so should get better!