force-refresh youtube iframe when changing speeds back to 1.0 in firefox

If Video Alpha is playing a YouTube video in Firefox in HTML5 mode, then when switching to speed 1.0 it will simply reload the iframe, instead of using the built-in method to change the speed. The fixes the bug temporarily, while the YouTube team fixes the bug internally in the API.

In any case, YouTube API reports the speed to be 1.0 in both cases (with bug fix and without it).

https://edx-wiki.atlassian.net/browse/BLD-108
https://edx-wiki.atlassian.net/browse/BLD-57

@rocha and @Lyla-Fischer please review.