User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:66.0) Gecko/20100101 Firefox/66.0

Steps to reproduce:

1. Go to this page:
   https://www.thinking3d.ac.uk/Echocardiography/

2. Scroll to the bottom, then back to the top.

Actual results:

Video <video> elements that loaded when you initially went to the page are now missing. This behaviour is consistent.

Expected results:

Videos should remain in place constantly.

This page works well in both Safari and Chrome.

Tested with Stable, Dev & Nightly releases.

I can reproduce on Firefox67.0b10 windows10.

STR:

1. Open https://www.thinking3d.ac.uk/Echocardiography/ in [TAB A]
2. Scroll to Fig 7 / Fig 8 so that these video will display into view
3. Open a new tab [TAB B]
4. Wait for 20 seconds
5. Go back to the tab [TAB A]

Actual Results:
Missing some video elements

Expected Results:
All video should display properly

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=ac1c8b26e69085a1ce075939533eb081b9e997ce&tochange=a773a42f4c001614c4ae826bc8ada7de29cea3e6

Regressed by:
a773a42f4c001614c4ae826bc8ada7de29cea3e6 alwu — Bug 1505972 - request audio data when entering 'loopingDecoding' state if decoding has ended r=jya

(BTW, I cannot reproduce on Nightly68.0a1 windows10)

Fixed window(at least windows10)
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=a42caa9f04fc41044437ac56eab6f6086c841d9f&tochange=126a59b083f619859b308f023bc5c8df49686b3d

ranvel,
It seems fixed in Nightly Build ID 20190510095015.
Can you please re-test with latest Nightly?

This is definitely fixed in: 68.0a1 (2019-05-12) (64-bit) on macOS. Thank you!