Fission Firefox Addon will allow you to combine the firefox progress bar with the firefox address bar and give firefox a safari style address bar.

Publisher Description :

Fission combines address bar and progress bar (Safari style). This makes the progress bar more visible and allows for a nice visual effect.

Safari style address bar for firefox

You can change the color of the progress bar by accessing the Fission option from Tools -> add-ons

Install Fission from here