A little. If a third party cookie is set while you're visiting a site, only that site will get the third party cookie back. Multiple sites can have embedded content making third party cookies, and with this change firefox will track where it was made and only give it back there.
With this change, it doesn't matter if it's first or third or whatever; cookies will only be given back to a site that matches much of what is in your location bar.
Honestly, if it has any level of air conditioning it will be a hit.
Current vehicles have windows and (sometimes) a fan.