I wanted to post this Question and answer it because I didn't know where to post this thread on a Mozilla website.
You can now install SPDY on your Apache server with mod_spdy by following these directions. I've done this, and in Chrome I can see the green lightning bolt on my site, just like on Twitter and Google. Yeah!
Firefox has an add-on that detects SPDY, but I installed it and still can't see that green lightning bolt. Is there any other way to detect SPDY on Firefox? I'm using FF 11 so that shouldn't be the issue.