Speeds up browsing a lot.

Really liked:
- insert mode (map i) that really works
- focusing input (gi) and using tab to switch between many of them
- toggle between previous tab (default ^, mapped it to q)
- vomnibar, especially tab search (T)
and of course the basic vim key bindings you expect from any vim extension.

Not being able to use Vimium-FF in Firefox native tabs bothers me a bit, sometimes Vimium-FF stops working on some pages, and the search (/) not highlighting results makes it pretty useless compared to the native Firefox search, but I've understood that they're limitations of the WebExtensions API rather than the fault of the extension developers. Overall very good, and that's why I give you 5/5 stars.