Sending the same video to the player doesn't start to play from the beginning

[SoftVision-CarmenFat]

[Affected versions]:

• Firefox Developer Edition 59.0b9
• Firefox Nightly 60.0a1 (02/16/2018)
• Min-Vid Shield Study Onboarding 0.4.7 - Shield Study

[Affected Platforms]:

• All Windows

[Prerequisites]:

• Latest Min-Vid v.0.4.7 Shield Study Onboarding ("active" or "activeAndOnboarding" variant) was previously installed on a clean profile.

[Steps to reproduce]:

1. Open the browser with the profiles from prerequisites and navigate to YouTube.
2. Send a video to the player.
3. Hover the same video and click the "Play Now" overlay button.
4. Observe the behavior.

[Expected result]:

• The selected video starts playback.

[Actual result]:

• The first video continues to play uninterrupted; a ping with "overlay_icon" event and "launch" method is sent to telemetry.

[Notes]:

• See also: 705
• This is also reproducible if the player is in the "Replay/Close" screen.
• Here is a screen recording of the issue: