I would highly recommend also reporting this issue to https://webcompat.com/, this is also a problem I see depending on the extension/video player that is loaded in the webpage.

Please post the bug issue after reporting it to that site (also part of Mozilla!) and we can follow up for you!

I am looking forward to that link and reply!

Firefox 42+ has a Tracking Protection feature that is enabled by default in Private Browsing mode. When you are in private browsing mode then Firefox can show a shield icon at the left end of the location/address bar that some content is blocked.

You can disable this feature in "Options/Preferences -> Privacy" or via the about:privatebrowsing page that get when you open a New Private Window.

• Options/Preferences -> Privacy: "Use Tracking Protection in Private Windows"

• https://support.mozilla.org/en-US/kb/tracking-protection-firefox
• https://support.mozilla.org/en-US/kb/control-center-site-privacy-and-security-firefox