Firefox nightlies do support Python. It's unfortunate that nobody wants to migrate away from JS though.
Does it mean lambdas or other anonymous functions? Python lets you close over names at any scope and define functions anywhere; you don't need the "lambda" keyword. Even if you want to only use lambdas, it's been shown that Python does not need statements, only expressions, to express everything, although you quickly turn your code into Scheme-soup. JS doesn't somehow improve on this.
Is it first-class functions? Python has those, just like JavaScript, although Python goes further, enabling you to have real bound methods, descriptors, properties, class methods, and all other kinds of fun.
Is it map, filter, and fold? Python's still got map, filter, and fold (foldl, called "reduce" in Python.) Python also has list comprehensions, borrowed from Haskell, as well as generator expressions, providing that valuable laziness that some functional languages value so much. And, in Python 3, there are set and dictionary comprehensions as well. JavaScript doesn't have comprehensions at all.
Is it referential transparency or immutability? Unlike JavaScript, Python refuses to allow you to edit the values of certain builtin types, like str and unicode.
So, uh, what did you mean, exactly?
Even if you were right, you could still make code that doesn't use these features fast, and slow back to interpreted if any of these features is used -- that's what JS JITs do when they see "with".
And finally, Lua is as dynamic as Python (both of which are, in my opinion, less dynamic than JS thanks to lexical binding). And Lua has been made significantly faster than any Python or JS implementation (Mike Pall's LuaJIT2)