By default, this simple utility displays a gray progress bar behind the URL that fills in from the left to right as the page loads. When the page fully loads, Fission's progress bar disappears.
If you want more glitz than the default gray, you can change the color of the progress bar, or choose a picture to display instead of a color. You can also choose to have the regular Firefox progress bar display to the right of the URL for a more Safari-like look. A helpful preview shows you what your choices will look like as you change the add-on's options, and a reset button will clear your picture and color choices to return to the default gray.
Fission does a good job of smoothly implementing its cosmetic changes. Pick it up if you want a more front-and-center progress meter.