1717890 - Slack hangs indefinitely when user interacts with some links

Status: RESOLVED WORKSFORME

(Web Compatibility :: Site Reports, defect, P3)

Description

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

Firefox 91.0a1 20210623095324 on Windows 8.1, jcristau also noticed similar behavior (should be on Linux)

If I go into MoCo's #berlin slack and click with the right mouse button on the email address posted today, the browser hangs until a slow script warning is shown. It still seems to be necessary to reload the slack tab after one stopped the script.

Profiler recording: https://share.firefox.dev/3gPVPFR

Comment 1

[:Gijs (he/him)]

Emilio, the same kind of issue (as bug 1640441) seems to be happening again here, judging by the profile - the jank period in the profile is entirely taken up by setTimeout combined with a mutation handler and a call into measureContents in the slack JS code which I expect flushes layout... I don't suppose you can take a look?

Comment 2

[Emilio Cobos Álvarez [:emilio]]

This is... not something easy to address on our side. This is just bug 1640441 again.

We do layout in app units, which are 1/60th of a CSS pixel, and can't be represented exactly by a float. Slack is relying on the values we return to be roundtripping / comparing in a way that they just can't right now.

I filed bug 1719314 to consider changing our internal representation of app-units since this bug keeps coming back and I found no open bug to track such thing, but that's a sad-ish change because 1/60 has some other nice properties.

I contacted slack on the #ext-slack-mozilla-performance channel anyhow, fixing this on their side should be trivial...

Comment 3

[Karl Dubost💡 :karlcow]

Needs Triage.

Comment 4

[Raul Bucata]

We appreciate your report. I was able to reproduce the issue. I have noticed this also to be reproducible on the "Get Started" page, when selecting a workspace or when accepting an invite for a workspace. It seems that the page returns an error regarding the mail used for signing in.

Tested with:

Browser / Version: Firefox Nightly 92.0a1 (2021-07-20) (64-bit)
Operating System: Windows 10 PRO x64

Notes:

1. Reproducible regardless of the status of ETP
2. Reproducible on the latest build of Firefox Nightly
3. Works as expected using Chrome

Comment 5

[Oana Arbuzov [:oanaarbuzov]]

I was not able to reproduce the issue on my side. Right clicking or hovering any links on Slack no longer hangs.
Also https://bugzilla.mozilla.org/show_bug.cgi?id=1640441 is fixed.

Tested with:
Browser / Version: Firefox Nightly 103.0a1 (2022-06-23)
Operating System: Windows 10 Pro

Sebastian can you still reproduce it?