Opera still does not play Twitter videos
Had the same thing with a Linux live usb, and found a fix -- make sure you have the following installed:
(You may need the i386 versions as well.)
Not sure which of these does the trick, but I too couldn't play any video on Twitter in Opera with a live usb. Then I fired up xplayer, which requested those extra multimedia plugins to be installed. After that, twitter had no trouble with any video.
Done that a few times now.