Anton/fix video in ff

**Description**

Fix start of YouTube Video playback in Firefox.

**Steps to reproduce**

When video starts playing from non-zero position:

1. click play button
2. pause
3. reload the page
4. verify that position is restored
5. click play button

**Jira issue**

[BLD-1057](https://edx-wiki.atlassian.net/browse/BLD-1057)

@valera-rozuvan please review.