pixel_player18778656 A Possible solution if you have been able to play webgl before but recently got the black bar with FPS: (i think this is for chrome, not sure if also works in other browsers)
use the menu button at the top right of the browser to choose Settings
Scroll to the very bottom of that page and choose the Advanced link
Under the System heading, locate and disable the option "Use hardware acceleration when available "
close e reopen chrome