975441 - Find out why having a chrome:// favicon for about:customizing makes entering customize mode so janky

Status: RESOLVED WONTFIX

(Firefox :: Toolbars and Customization, defect)

Description

[Mike Conley (:mconley) (:⚙️)]

STR:

1) On Windows, enter customize mode via the menu button. Notice how janky that is.
2) Now, instead of closing customize mode, switch out of it by choosing another tab. Then switch in by choosing about:customizing again.

ER:

Those two ways of switching in and out should be equivalent.

AR:

They're not! Opening the about:customizing via the menu panel is super janky.

I've traced this down to the favicon in aboutCustomizing.xul. It looks like if I replace the chrome:// URL with a standard web URL (I used https://www.google.ca/favicon.ico#-moz-resolution=16,16), things get much, much smoother.

So how come loading a chrome URL is worse? Are we doing sync IO on the main thread to load it?

Marking as a P2 because solving this is probably our best bet at making the customization transition performance reasonably smooth.

Comment 1

[Mike Conley (:mconley) (:⚙️)]

I'm going to push a patch to try with no favicon to see how this affects CART.

Comment 2

[Mike Conley (:mconley) (:⚙️)]

Something is strange here - on one machine, switching out the favicon made a pretty big difference. On another, not so much. :/ And then, on that first machine, putting the old favicon back didn't slow things down.

P-'ing until I figure out what's going on here.

Comment 3

[Manish Goregaokar [:manishearth]]

(In reply to Mike Conley (:mconley) from comment #0)

> So how come loading a chrome URL is worse? Are we doing sync IO on the main
> thread to load it?

It's on the main thread, though it seems to be async (no special treatment for chrome://): 

http://mxr.mozilla.org/mozilla-central/source/toolkit/components/places/AsyncFaviconHelpers.cpp#529


(already mentioned this in IRC, just leaving breadcrumbs for others)

Comment 4

[Mike Conley (:mconley) (:⚙️)]

This turned out, I think, to be a bit of a red herring. While it's true that having a favicon adds a tiny amount of time to our CART results, I don't think it's really worth pursuing solutions to this one at this time.