It's probably on your end as the voice is done in the browser. Which OS are you on? The browsers may require some OS functionality for the speech synthesis to work.
Did work on Chrome - two problems: one was a sound cut off before the end and so I entered the wrong number; second the last number read finished the game but without any time for entering the number, it deducted a mark. A further game (different language) ended before I finished and didn't tell me the last answer.
