Fix Default Image Blocking Layouts in Mozilla Thunderbird — MJML Framework Guide for WCAG Accessibility Violations
Accessibility failures prevent screen readers from navigating templates, isolating disabled subscribers and increasing unsubscribe rates. Below is the targeted integration guide to fix Default Image Blocking Layouts inside Mozilla Thunderbird templates when using MJML Framework.
Technical Breakdown
Mozilla Thunderbird uses the Gecko which lacks support for standard rendering rules. This causes Default Image Blocking Layouts elements to break or collapse when rendering templates.
MJML Framework Behaviors
The MJML transpilation compiler parses dynamic columns and wraps them in custom HTML conditional tags. If you paste direct tables or VML code blocks inside an MJML layout without proper escaping, the MJML compiler will try to clean the code, resulting in stripped Outlook namespaces and broken layouts. Inject correct table roles (role='presentation') and keep color pairings above the WCAG AA contrast threshold of 4.5:1.
Remediation Code Block
To resolve this, always define explicit width and height attributes on your images to preserve their layout boxes when blocked. Add robust alternative (ALT) text styled with CSS font-sizes and colors, and encode vital brand logos directly as Base64 data URIs. In your MJML Framework campaign manager, make sure you configure your links to run via {{unsubscribe_link}}.
<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAADIA..." width="150" height="40" alt="Company Logo" style="display: block; font-family: sans-serif; font-size: 14px; color: #111111; font-weight: bold; border: 0;">Live Code Sandbox Test
How to Deploy inside MJML Framework
Copy the fixed VML or table wrapper code block from the remediation box above.
Wrap the entire RenderOps corrected table block inside an '<mj-raw>' tag block. This tells the MJML compiler to bypass parsing on this segment, exporting the exact conditional statements into the final HTML output.