Firefox for Android can continue playing video even if you switch to another tab or app. However, sites can detect these user actions with the Page Visibility API and the Fullscreen API. This add-on is designed to block events and properties exposed by the APIs.

Add-on code: MIT.

"Glasses" icon used in the logo by rahmatmasiv from the Noun Project under the CC BY 3.0 US.

The add-on injects a content script to replace the properties exposed, and stops events from propagating when applicable.

The add-on blocks visibilitychange event, and set document.hidden to be always false and document.visibilityState to be forever visible.

The add-on doesn't generally override the Fullscreen API because at the moment this is not required and the original implementation caused some broken UI after existing fullscreen. As a site-specific workaround, we do however block fullscreenchange events on Vimeo to prevent playback from stopping when exiting fullscreen.

Some pages stop playback if they don't detect any user activity for a certain amount of time. To avoid this, the add-on ensures that the time of the last user activity is regularly updated.

As a demonstration, the content script currently injects itself to the following sites:

• youtube.com and youtube-nocookie.com
• vimeo.com