This is an addon to play online videos with subtitles. When you can go to any online video streaming site(such as Youtube, Metacafe, Megamovies …. ), this will allow you to play with subtitles. Watch movies TV series available on other sites with your customized subtitles.
You can simply switch it on/off from the tool button at the below panel and it will start grabbing files you can play with subtitles.
Watch a full demonstration of the add-on in youtube at How to watch movies with subtitles online