How to reproduce:
1. Open user's attached "VIDEO_TEST_unity" project
2. Open the "SampleScene" Scene
3. Open the Build Settings (File->Build Settings...)
4. Add the opened Scene to the Scenes in Build list (by pressing the "Add Open Scene" button in the Build Settings window)
5. Build And Run the project
6. When the Build is running press on the black square

Expected results: The video does not become black in between the loops
Actual result: The video is showing black view in between the loops

Reproducible with: 2019.3.14f1, 2019.4.8f1, 2020.1.3f1, 2020.2.0a20
Not reproducible with: 2019.3.0a1, 2019.3.0a2
Could not test with: 2018.4.0f1 because of the "Assembly has reference to non-existent assembly" error, 2019.3.0a3, 2019.3.13f1 because the video won't play

Notes:
- Happens only on Firefox, does not happen on Chrome and Edge