Kilotest: Diagnoses of attribute value invalid violation by HTML element 412 on Mozilla Foundation page

Basics

About the page

• URL: https://www.mozilla.org/en-US/
• Tested 32 days ago on 2026-09-08 at 04:02 by job 260908T0359-xmh
• Summary of results:
  • Rule engines:
    • Called: 12
    • Were able to test: 12
    • Reported any rule violations: 11
  • Violations: 753
  • Violators: 192
  • Issues: 47
• Download the full technical report (JSON)

About the issue

• Why it matters: Item behaves improperly
• Priority: highest
• Related WCAG standard: 1.3.1
• Reported by 1 rule engine (Html Checker API)
• Violations: 6
• Violators: 6

About the violator

• Tag name: SOURCE
• Text: [not applicable]
• Start tag: <source media="(max-width: 1311px)" srcset="https://www.mozilla.org/media/cms/images/image1.2e16d0ba.fill-400x200.jpg 400w, https://www.mozilla.org/media/cms/images/image1.2e16d0ba.fill-600x300.jpg 600w, https://www.mozilla.org/media/cms/images/image1.2e16d0ba.fill-800x400.jpg 800w, https://www.mozilla.org/media/cms/images/image1.2e16d0ba.fill-1000x500.jpg 1000w, https://www.mozilla.org/media/cms/images/image1.2e16d0ba.fill-1200x600.jpg 1200w, https://www.mozilla.org/media/cms/images/image1.2e16d0ba.fill-1400x700.jpg 1200w" sizes="(min-width: 768px) calc((100vw - 32px) / 2), calc(100vw - 32px)" width="1400" height="700">
• XPath: /html/body/div[2]/main[1]/section[1]/div[1]/div[1]/div[2]/div[1]/picture[1]/source[1]
• Bounding box: x = 736, y = 2726, width = 0, height = 0
• Reported by Html Checker API

Diagnoses

Here is how rule engines diagnose the attribute value invalid issue for HTML element 412 of the Mozilla Foundation page.

1. Bad value for attribute srcset on element source: Width for image https://www.mozilla.org/m…e16d0ba.fill-1400x700.jpg is identical to width for image https://www.mozilla.org/m…e16d0ba.fill-1200x600.jpg.

   Rule engine: Html Checker API (World Wide Web Consortium)