The Text Options button can be found above the Bible text with the other settings options (e.g. Share, Print, etc.). These options allow you to adjust the way that the Bible passage is displayed in your web browser by toggling them on or off.
Clicking or tapping the Text Options button (which looks like a gear) lists these options that can be toggled on or off:
Clicking to add a check mark will cause that option to be displayed. Unchecking the option removes it from the passage. Keep in mind that not all Bibles have all these options.