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Intent to prototype and ship: lazy load images

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Hiroyuki Birchill Ikezoe

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Feb 10, 2020, 9:22:37 AM2/10/20
to dev-pl...@lists.mozilla.org
In Firefox 75, I intend to turn lazy load images on by default.

Summary: lazy load images improves initial page load performance by
deferring loading images which are out of viewport, it also reduces network
traffic.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1542784

Standard: https://github.com/whatwg/html/pull/3752

Platform coverage: all

Preference: dom.image-lazy-loading.enabled

Devtools bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1611387

Other browsers: Chrome has shipped it since 76. WebKit is now implementing
it [1]

web-platform-tests:
https://wpt.fyi/results/loading/lazyload?label=experimental&label=master&aligned

Secure contexts: this feature is not restricted to secure contexts. I don't
see any reasons to restrict it in secure contexts. If you have concerns,
please let me know.

Is this feature enabled by default in sandboxed iframes?: no, as of now
there is no proposed flag to enable this feature in sandboxed iframes.

Bug to turn on by default:
https://bugzilla.mozilla.org/show_bug.cgi?id=1613611

hiro

[1] https://bugs.webkit.org/show_bug.cgi?id=200764

Boris Zbarsky

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Feb 10, 2020, 9:42:13 AM2/10/20
to
On 2/6/20 5:26 PM, Hiroyuki Birchill Ikezoe wrote:
> Is this feature enabled by default in sandboxed iframes?: no, as of now
> there is no proposed flag to enable this feature in sandboxed iframes.

But is it disabled by default there? I would assume not, unless it's
specifically gated on sandboxing state...

-Boris

Anne van Kesteren

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Feb 14, 2020, 2:48:34 PM2/14/20
to Hiroyuki Birchill Ikezoe, dev-platform
On Mon, Feb 10, 2020 at 3:22 PM Hiroyuki Birchill Ikezoe
<hikezoe....@mozilla.com> wrote:
> Is this feature enabled by default in sandboxed iframes?: no, as of now
> there is no proposed flag to enable this feature in sandboxed iframes.

I think the answer to this question is more complicated. It's disabled
if scripts are disabled, but if scripts are enabled, image lazy load
is enabled, right?

Hiroyuki Birchill Ikezoe

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Feb 14, 2020, 2:48:37 PM2/14/20
to Anne van Kesteren, dev-platform
Right. Thanks for the clarification.

hiro

Hiroyuki Birchill Ikezoe

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Feb 18, 2020, 9:20:49 AM2/18/20
to Boris Zbarsky, dev-platform
To be more precise, lazy loading is disabled in documents where scripting
is disabled.
Though I don't know the exact conditions where scripting is disabled, by
default lazy loading is disabled without `allow-scripts` keyword.

hiro
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