1536789 - Consider interrupting html parser's flush loop before script execution if there is a possible first contentful paint pending

Status: NEW

(Core :: DOM: HTML Parser, enhancement, P2)

Description

[Olli Pettay [:smaug][[e-mail]]]

Attachment: script_interrupt_parser.diff

There are pages where there is first some content and then some <script>s, and we often end up executing those scripts before painting. That leads to worse first contentful paint times.

Comment 1

[Olli Pettay [:smaug][[e-mail]]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=aede3216461c9c3924ba03a2bdbe7ca131d8fcc2

Comment 2

[Olli Pettay [:smaug][[e-mail]]]

Some sites really like this https://i.ibb.co/PML4SbD/image.png
but then Facebook doesn't.

It is possible that we should paint even less often during pageload to not regress Facebook.
(FB uses heavily animation frame callbacks.)

Comment 3

[Olli Pettay [:smaug][[e-mail]]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=cbdb281ee34b5f83ded39eaaabd99772121a4df7

The idea came the we should interrupt only if we haven't painted for awhile.