1530479 - Convert more parts of browser_startup.js to an allow list

Status: NEW

(Firefox :: General, enhancement, P3)

Description

[:Felipe Gomes (needinfo for replies!)]

As I was filing bug 1530478, I thought "why wasn't this caught by browser_startup.js?", and it turns out it's because that's still a blacklist: [1]

We should try to convert at least the "before opening first browser window" and "before first paint" parts to whitelist as we're doing a large effort of improving startup perf.

[1] https://searchfox.org/mozilla-central/rev/b10ae6b7a50d176a813900cbe9dc18c85acd604b/browser/base/content/test/performance/browser_startup.js#54

Comment 1

[:Gijs (he/him)]

(p2 rather than p1 because per the discussion in the meeting I wonder if we should do more work here to actually reduce the pile of JSMs, before making this change)

Comment 2

[:Felipe Gomes (needinfo for replies!)]

Attachment: modules open before opening first window.txt

Indeed, the list is very large. Here's just all the modules that the test report as open before opening the first window. There are 108 modules.

(note: these modules could have been loaded during that step or the earlier steps.. I didn't filter that)

Comment 3

[Mike Conley (:mconley) (:⚙️)]

Attachment: whitelist.diff

mandycheang started looking at this, but is halting work to focus on school stuff, so attaching her WIP here.