While progress bar actually reveals page loading actions which is similar in case of Firefox and Chrome but it’s a bit different for Opera, Opera progress bar shows the page elements that are loading on right side of the address bar by showing number of elements loading and needs to load.
Some times it does irritate you as you keep looking at elements count and the page never loads completely, if page is loaded completely reload button does appear on the navigation bar. If you don’t want to see the progress bar/indicator on Opera here is how to turn off /disable it.
Disabling Opera Progress bar
1 .Press Shift +F12 to get the Appearance dialog window
2. Select Toolbars tab, and for the progress bar from drop down menu choose Off , click Ok to save changes.
3. Opera progress indicator disappears , to get back again select Simple option for the progress bar.