Almost as good as the Chrome version, though there are some things that are a little broken.

- "Hamburger" menu doesn't do anything (but I prefer it closed anyway).
- Feels a lot more sluggish than in Chrome (opening the menu, the settings page, etc)
- Rich notifications aren't really that rich without buttons, but I think that's Firefox's fault for not providing the ability.

Of those, the lack of good notifications is the real bummer. Hopefully that improves in time.