1650250 - Slow startup/high CPU use when restoring Firefox session with about:newtab as active tab in all windows

Status: NEW

(Firefox :: Session Restore, defect)

Description

[Asif Youssuff]

Basic information

Steps to Reproduce:

1. Have a lot of Firefox windows and tabs
2. Navigate to about:newtab in every open window (15)
3. quit Firefox, restore session

Expected Results:

Firefox should open in 11 seconds or less (Chromium manages this, so using this as a baseline) with no visible loading occurring.

Actual Results:

Firefox takes nearly a minute to load.

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More information

This isn't a stress test by any means - I regularly open a Firefox session with 15 windows, and with many extensions enabled. For this test, for troubleshooting purposes, I disabled my extensions and navigated to about:newtab to try to get a good baseline for a best case scenario with this many windows.

The fact that Chromium can open 15 windows with the Bing newtab (which has live content loaded) in a short amount of time makes this is the number to beat.

Profile URL: https://share.firefox.dev/2BqHPjY

Basic systems configuration:

OS version: Ubuntu 20.10

GPU model: Intel(R) HD Graphics 630 (KBL GT2)

Number of cores: 4

Amount of memory (RAM): 24GB

Thanks so much for your help.

Comment 1

[Asif Youssuff]

Attachment: about:support

Comment 2

[Andrew Creskey [:acreskey]]

:sefeng noticed that numerous setTimeouts were deferred for up to 40s.
Perhaps the lack of idle time on the main thread is making this quite problematic.

Notice how the pocket network requests do not start until ~42 seconds.

Comment 3

[Mike Conley (:mconley) (:⚙️)]

A significant chunk of this profile appears to be spending time in session restore, restoring the windows: https://share.firefox.dev/32Nj0cZ

Comment 4

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:mikedeboer, could you have a look please?

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