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Do you have a Firefox version of this?

No, sorry. The code should be pretty easy to port, if you want to give it a go.

Can I port it to FF?

From the parent comment: yes.

Absolutely!

Is this not a perfect use-case for greasemonkey/tampermonkey? Browser independence FTW

Orion supports FF and Chrome extensions, if you're in the market for a (good) Safari clone.