Fix Gmail Line-Height Shifts in Mozilla Thunderbird — SendGrid 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 Gmail Line-Height Shifts inside Mozilla Thunderbird templates when using SendGrid.
Technical Breakdown
Mozilla Thunderbird uses the Gecko which lacks support for standard rendering rules. This causes Gmail Line-Height Shifts elements to break or collapse when rendering templates.
SendGrid Behaviors
SendGrid's template parser automatically injects custom style tags that can override inline styles. Always use inline style definitions and define clear target widths. Inject correct table roles (role='presentation') and keep color pairings above the WCAG AA contrast threshold of 4.5:1.
Remediation Code Block
Define line-height as a unitless ratio (e.g. line-height: 1.4) or in explicit percentages (e.g. line-height: 140%). Avoid mixing em and px units, and apply the styles directly to the containing td or span tags containing typography. In your SendGrid campaign manager, make sure you configure your links to run via {{{unsubscribe}}}.
<p style="font-size: 16px; line-height: 22px; margin: 0; mso-line-height-rule: exactly;">Typography Paragraph</p>Live Code Sandbox Test
How to Deploy inside SendGrid
Copy the fixed VML or table wrapper code block from the remediation box above.
Open SendGrid Design Editor, toggle the view mode to Code Editor, or insert a custom 'Code' module block inside your drag-and-drop layout. Drop the corrected code inside the box.