Fission
With Fission you can add extra functionality to your address bar in Firefox. You can either transform the address field to a progress bar and show the progress behind the address, or you can add a progress bar to the right of the address.
It is also possible to show connection status at the right of the address bar, which tells you what currently is loading on the website, like if you are watching a streamed video.
I recommend this add-on because it adds extra functionality( to your already awesome web browser), and it looks really good.
Link to the add-on: