2011628 - Sniff <!-- as HTML to match Chrome

Status: VERIFIED FIXED

(Core :: Networking, enhancement, P2)

Description

[Valentin Gosu [:valentin] {{PTO until Nov 1st}}]

According to mimesniff <!-- should be followed by space or > to be sniffed as HTML. But Chrome does it regardless.
This bug is to match that behaviour (with a pref)

Comment 1

[Valentin Gosu [:valentin] {{PTO until Nov 1st}}]

Attachment: Bug 2011628 - Add tentative WPT for sniffing <!-- as HTML when not followed by space or > r=#necko

Comment 2

[Valentin Gosu [:valentin] {{PTO until Nov 1st}}]

Attachment: Bug 2011628 - Sniff <!-- as HTML to match Chrome r=#necko

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/f4d5c2a51c84
https://hg.mozilla.org/integration/autoland/rev/ba8b7fc9f987
Add tentative WPT for sniffing <!-- as HTML when not followed by space or > r=necko-reviewers,kershaw
https://github.com/mozilla-firefox/firefox/commit/1db684dd9b7c
https://hg.mozilla.org/integration/autoland/rev/621e87a0bb78
Sniff <!-- as HTML to match Chrome r=necko-reviewers,kershaw

Comment 4

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/57285 for changes under testing/web-platform/tests

Comment 5

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/ba8b7fc9f987
https://hg.mozilla.org/mozilla-central/rev/621e87a0bb78

Comment 6

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot

Comment 7

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot

Comment 9

[Valentin Gosu [:valentin] {{PTO until Nov 1st}}]

Attachment: Bug 2011628 - Add tentative WPT for sniffing <!-- as HTML when not followed by space or >

Original Revision: https://phabricator.services.mozilla.com/D279843

Comment 10

[Phabricator Automation]

firefox-beta Uplift Approval Request

• User impact if declined: Webcompat issues when pages are served without a content type, and they start with a <!--comment. Note no space between !-- and the text.
  See bug 2006569.
• Code covered by automated testing: yes
• Fix verified in Nightly: yes
• Needs manual QE test: yes
• Steps to reproduce for manual QE testing: See bug 2006569 comment 0
• Risk associated with taking this patch: low
• Explanation of risk level: Fixes a regression. Aligns Firefox sniffing of HTML with other browsers. Fix is really simple and behind a pref
• String changes made/needed: none
• Is Android affected?: yes

Comment 11

[Valentin Gosu [:valentin] {{PTO until Nov 1st}}]

Attachment: Bug 2011628 - Sniff <!-- as HTML to match Chrome

Original Revision: https://phabricator.services.mozilla.com/D279844

Comment 12

[Alexandru Trif, Desktop Test Engineering [:atrif]]

Reproduced the issue with Firefox 148.0a1 (2025-12-17) on Windows 11. The https://ghosttogether.net/change/password webpage is displayed in html code when opened.
The issue is verified fixed with Firefox 149.0a1 (2026-01-22) on Windows 11, macOS 15 and Ubuntu 24. While the network.mimesniff.non_standard_html_comment pref it's true (as default) the https://ghosttogether.net/change/password page is correctly displayed. Turning network.mimesniff.non_standard_html_comment will reproduce the issue again.

Comment 13

[Pulsebot]

https://github.com/mozilla-firefox/firefox/commit/7fec64dae82b
https://hg.mozilla.org/releases/mozilla-beta/rev/2afa35920951
https://github.com/mozilla-firefox/firefox/commit/1c9e8f2e4fe4
https://hg.mozilla.org/releases/mozilla-beta/rev/76dea93dcbc3

Comment 14

[Alexandru Trif, Desktop Test Engineering [:atrif]]

Verified fixed with 148.0b7 (20260125090536) build on Windows 11, macOS 14 and Ubuntu 24. While the network.mimesniff.non_standard_html_comment pref it's true (as default) the https://ghosttogether.net/change/password page is correctly displayed. Turning network.mimesniff.non_standard_html_comment to false will reproduce the issue again.