This extension adds a tiny permanent progress bar (ProgressBar) to YouTube. The height of this progress bar can be configured in the options page. When YouTube's default progress is shown the permanent one is hidden (obviously!). This extension adds this tiny progress bar even in the fullscreen mode!
The idea is to know the current progress status of the playing video. With this extension, you can take a look at the bottom of the player any time even in the fullscreen mode to find the percentage of the video that is passed.
If the progress bar is to narrow for you, go to the options page to configure the height.
Like the default progress bar, the permanent progress bar displays both progress and loaded percentages.