1388910 - remove support for '-moz-user-modify' CSS property

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, task, P3)

Description

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

Based on https://lists.w3.org/Archives/Public/www-style/2015Apr/0406.html I think we should consider removing support for the -moz-user-modify CSS property.

The original spec for this was:
https://www.w3.org/TR/2000/WD-css3-userint-20000216#user-modify

It seems like the only thing we do with the property is, under some conditions, change whether the caret is visible:
https://searchfox.org/mozilla-central/rev/c329d562fb6c6218bdb79290faaf015467ef89e2/layout/base/nsCaret.cpp#549

This doesn't particularly seem to match the intent of the property, and makes it seem like we should probably remove the caret-related behavior since it doesn't seem to do anything else.

If we remove it, we might need something else to control the caret behavior, though, since the property does appear to be used to control caret visibility in our UA style sheets.

Alternatively, we could change the property to be accessible only from UA style sheets, and stop exposing it to the Web.

Comment 1

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1388910 - Remove -moz-user-modify property. r=#style,#layout

We successfully unshipped it in bug 1920118.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/130794a57298
Remove -moz-user-modify property. r=dshin

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/comm-central/rev/f260cbb2bd1c
no longer package bin/res/designmode.css for Thunderbird. rs=bustage-fix

Comment 4

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

https://hg.mozilla.org/mozilla-central/rev/130794a57298

Comment 5

[Mayank Bansal]

This lead to a 2.8% improvement on Sp3-editor-tiptap/Highlight/Sync/opt fission.

Edit:
This is effectively bringing the regression from bug 1934501 back to baseline. (Focus on this perfherder graph.
Baseline: 32ms
Post-regression from bug 1934501 : ~34ms
Post improvement from this bug: 32ms

Comment 6

[Alex Finder]

(In reply to Pulsebot from comment #2)

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/130794a57298
Remove -moz-user-modify property. r=dshin

Perfherder has detected a browsertime performance change from push 130794a57298f50adb259e805866e563ec72cf63.

Improvement:

Ratio	Test	Platform	Options	Absolute values (old vs new)	Performance Profiles
6%	speedometer3 Editor-TipTap/Highlight/Sync	windows11-64-shippable-qr	fission webrender	33.52 -> 35.45	Before/After

This was initially opened as a regression alert, but is actually an improvement as Mayank pointed out in the previous comment.