What's matter in the end, "Does the browser (the tool) could do their 99% jobs they promised in real world people use". Just up to 99%, nothing is perfect in this world.
You're right - and I just want to mention, that Amazon Prime videos are played also. I tried this after testing built in videos...
[Regression] Twitter web notifications do not work (VB-26048)
Can you try that out and confirm whether it works for you?
Disclaimer: Don't update your current Vivaldi! Install new instance as "standalone", so that it doesn't interfere with your current installation. You can easily get rid of it later by removing the folder where it was installed.
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