View source for Firefox/Block Playback

=Overview=
Videos which autoplay in the background will now have their load deferred until the tab is visible for the first time -- this avoids autoplay during session restore and premature playback. This means no more "Where's that sound coming from?" moments when an ad for instance decides to autoplay in a tab you've specifically opened in the background.
Resources will still be preloaded if indicated but Firefox will delay the start of playback until you actually visit the tab. Once a tab / RenderFrame has ever played media before, it's allowed to continue to autoplay/autoload indefinitely; this is to support playlist type applications. This feature prevents obviously user annoyance but also conserves power as Firefox will only consume power once the tab is foregrounded.

==Issue==
This mechanism will also block notification sounds from websites such as Facebook or Gmail if a user open the tab but haven’t visited it yet. There are also users who want to open new tab for music without needing to visit the tab. The mechanism will force users to visit the tab for the music to start playing.

===Other Resources===
* [https://goo.gl/0dylCY Meeting Minute]

=='''MVP Scope'''==
Meta Bug: [https://bugzilla.mozilla.org/show_bug.cgi?id=1308154 1308154 - (block-autoplay-media) [meta<nowiki>]</nowiki> Block autoplay media until the tab is visible at first time]


<bugzilla>
    {
        "blocks":"1308154",
        "status":["NEW","REOPENED","UNCONFIRMED","ASSIGNED","RESOLVED","VERIFIED","CLOSED"],
        "include_fields": "id, summary, status, target_milestone, resolution, assigned_to, depends_on, blocks, whiteboard"
    }
</bugzilla>

= Schedule =
Targeting: '''Firefox 52'''

=Team=

Eng: Alastor, JW, Kaku

Program Management: Blake, Josh

UX: Mark, Morpheus 

QA: SoftVision