Note: For this tweak I recommend using the ChromEdit Plus
This tweak allows you to change the color of the progress bar in your status bar. Simply add these lines to your userChrome.css file located in your profile folder:
/* Change the progress bar color */
-moz-appearance: none !important;
background-color: #660000 !important; }
To specify the color, choose your color here and note the six-digit hex code. Within the code you have copied from above to your userChrome.css file, replace ‘660000’ with the six-digit hex code for the color you have chosen. Make sure you include the ‘#’ in front of the six-digit hex code. When you are done editing your userChrome.css file, close and restart Firefox and the changes should take effect right away. This tweak works with most versions of Firefox.