How to reproduce:
1. Open the project “IN-105305“
2. Build&Run the “BugRepro” scene
3. Run the application in the Firefox browser
4. Observe that the video's background is opaque
5. Under Project Settings/Player/Other Settings set Color Space to “Gamma“
6. Build&Run the “BugRepro” scene again
7. Observe the change in video transparency

Expected result: Video is transparent on both Color Spaces
Actual result: Video has black background on “Linear“ Color Space

Reproducible with: 2021.3.52f1, 2022.1.0a1, 2022.3.63f1, 6000.0.51f1, 6000.1.7f1, 6000.2.0b5

Reproducible on: Windows 10 (user reported), Windows 11 Enterprise
Not reproducible on: No other environments tested

Workaround:
- use “Gamma“ Color Space

Notes:
- Reproducible on Google Chrome 138.0.7204.50 (64-bit)
- Reproducible on Firefox 139.0.4 (64-bit)
- Reproducible on Microsoft Edge 138.0.3351.55 (Official build) (64-bit)