Firefox encodes URI for pushState -- workaround?

Question

In Firefox, when you use window.history.pushState, it automatically encodes the URI for you. In other browsers (IE, Chrome, Safari), it does not. So, if you want your URI encoded, you need to do it yourself (i.e. with encodeURI) -- unless you're using Firefox.

To see this for yourself, run this code in the Chrome dev console and the Firefox dev console:

window.history.pushState({},'asdf','#spaces or percent twenties');
location.href;
// Firefox: "...#spaces%20or%020percent%20twenties"
// Other browsers: "...#spaces or percent twenties"

The W3 spec for window.history.pushState doesn't specify to encode the URI, so I think this is an error on Firefox's part.

In the meantime before this is unified, though, I need a workaround to make Firefox play nice. Any suggestions?