I'm somewhat disappointed that there is no Firefox version. However, given that the author most likely uses his extension, I can see what might have happened.
I always thought firefox and chrome share a standard where you could build one extension and use them on both platforms?
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...
To your point, the Orion webkit-based browser for MacOS supports both:
AFAIK, the only webkit browser to do so.