There's one for Google and one for Twitter, too. Both are not maintained by Mozilla, but by third-party devs, but the code changes are straight-forward (replace

There's one for Google and one for Twitter, too. Both are not maintained by Mozilla, but by third-party devs, but the code changes are straight-forward (replace domains, make Google container tabs red by default instead of blue, use different icon). I use them for several months, and I'm pretty happy about them.