From a long time There is a theme for Firefox that is called MacOSX Theme This is used for make Firefox appearance like Mac. The bad news about this add-ons is that this plugin doesn’t maintain as good as it should be. Now this add-ons theme doesn’t work current Firefox.
Don’t worry. You can got it f1beta.com/macosxthemefirefox_4-1.8.1-fx.xpi
Note:- This plugin is work of https://addons.mozilla.org/en-US/firefox/user/golf-at/ and found online https://addons.mozilla.org/en-US/firefox/addon/macosx-theme-firefox-4/?src=api
I just patch it for people who have problem with installing it on latest Firefox.
You can still use This theme from original site with this hack https://addons.mozilla.org/en-US/firefox/addon/checkcompatibility/ this plugin make the unsupported plugin worked.