■公式ナイトリービルド (使用は自己責任で)
https://www.mozilla.org/ja/firefox/channel/desktop/#nightly

■非公式ビルド (使用は自己責任で)

Firefox Mac Community Builds
http://firefoxmac.furbism.com/

Firefox 4.0 build for Mac OS X 10.6 (64bit, GCD, Clang) • mozillaZine Forums
https://forums.mozillazine.org/viewtopic.php?f=42&t=1514615

tenfourfox
https://code.google.com/archive/p/tenfourfox/

■Wikipedia
https://ja.wikipedia.org/wiki/Mozilla_Firefox