1493218 - GitHub PDF render is about 6x slower in Firefox compared to Chrome or Edge

Status: NEW

(Core :: Graphics, defect, P3)

Description

[Chris Peterson [:cpeterson]]

GitHub uses PDF.js to render PDF files, but it is much slower in Firefox than Chrome and Edge.

STR:
1. Load https://github.com/isocpp/CppCoreGuidelines/blob/master/docs/Lifetime.pdf

EXPECTED RESULT:
On my Windows 10 laptop, Chrome renders the PDF in about 4 seconds. Edge renders it in about 6 seconds.

ACTUAL RESULT:
Firefox 62 and 64 Nightly render it in about 27 seconds.

Here is a Gecko profile of 64 Nightly. It looks like most of the time is spent in D2D.

https://perfht.ml/2QQaim7

Comment 1

[Lee Salzman [:lsalzman]]

Bas, looking at the profile, it seems we're spending lots of time inside DrawTargetD2D, mostly in D2D both from flushing inside FillGlyphs, and because it's seemingly creating a lot of expensive layers too inside PushClip (which is getting called from the JS). Ideas?

Comment 2

[Daniel Holbert [:dholbert]]

FWIW: on Linux Nightly, it renders in about 3 seconds.

Comment 3

[Chris Peterson [:cpeterson]]

This does seem to be a Windows-specific problem. On my Mac, the PDF renders in less than two seconds.

I forgot to mention in the STR:

2. Scroll to the bottom of the PDF and wait for the last page (45) to finish rendering.

Comment 4

[Bas Schouten (:bas.schouten)]

This seems to still render much more slowly to me on Firefox vs Chrome with WebRender.