Fix Gmail Line-Height Shifts in Mozilla Thunderbird — Campaign Monitor 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 Campaign Monitor.
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.
Campaign Monitor Behaviors
Campaign Monitor wraps custom blocks in dynamic edit tags, which can break the column flow inside Outlook. Ensuring correct class names is essential. 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 Campaign Monitor 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 Campaign Monitor
Copy the fixed VML or table wrapper code block from the remediation box above.
In Campaign Monitor, click the 'Source' button on your selected editable text region, or edit the template code files directly. Ensure you append the 'class="cs-editable"' flag if you need inline editing later.