It will only work with a Greasemonkey-compatible extension because Chrome doesn't support all the GM_* functions or headers I'm using. In Chrome, you'll have to use Tampermonkey. If I get time I may see if there's a way to make it more portable by not using GM_* functions, but for now I don't think t here's a way around it.

Did you try to install it as a native chrome extension, or using Tampermonkey?

@BrockAdams I've updated my example above to show the entire script, which you can see does not use any GM_* functions (or any functions at all except for SE.init).

Yep, this is TM 3.2.3444, and I don't have any @grant directives. I'll give FF a try.