Video remains in loading state after pausing it at its last second

[Softvision-CristinaBadescu]

[Notes]:

• When testing this, you may also encounter #537 issue.

[Affected versions]:

• Firefox 58.0 and up

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Latest Min-Vid Shield Study (Onboarding 0.4.7) was previously installed on a clean profile.

[Steps to reproduce]:

1. Open Firefox browser with the profile from prerequisites.
2. Navigate to a video YouTube link, eg. https://www.youtube.com/watch?v=BUQYHVo1qB4.
3. Click the "Play now" button.
4. When the video is at its last second, wait a brief moment and pause it.
5. Observe the behavior.

[Expected result]:

• The "Close/Replay" screen is displayed. or
• The video is paused.

[Actual result]:

• The video is loading, and the "Play/Pause" button is unactionable.

[Additional notes]:

• You can overpass this issue by clicking the progress bar.
• This issue is also reproducible with latest Min Vid version 0.4.8 from Test Pilot experiments page.
• Here is a screen recording of the issue: