You can clone with
Around the Firefox 4 timeline, I made the Mac toolbar button appear in grey, as suggested:https://blog.mozilla.org/addons/2010/12/02/toolbar-buttons-in-firefox-4/
But nobody else seems to do this. It's difficult to tell the difference between greyscale monkey and faded greyscale monkey for enabled/disabled status. Take that and anything else relevant into account.
Remove mac-specific style that greys the toolbar button.