Fix Gmail Line-Height Shifts in Mozilla Thunderbird — Salesforce Marketing Cloud (SFMC) Guide for Editorial & Content Newsletters
Editorial newsletters rely on content layout readability and structural text spacing. If fonts default to Times New Roman or layout borders break, subscriber engagement metrics suffer. Below is the targeted integration guide to fix Gmail Line-Height Shifts inside Mozilla Thunderbird templates when using Salesforce Marketing Cloud (SFMC).
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.
Salesforce Marketing Cloud (SFMC) Behaviors
SFMC's Content Builder wraps block exports in div frames that can break conditional comments. Additionally, AMPScript calls for personalizations can trigger parsing errors if they are inside MSO conditional comments. Ensure your AMPScript tags are evaluated *outside* the VML blocks. Keep your editorial body clean. Strip redundant CSS class definitions using Vaporize to ensure the newsletter stays under Gmail's 102KB clipping ceiling.
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 Salesforce Marketing Cloud (SFMC) campaign manager, make sure you configure your links to run via %%unsubscribe_url%%.
<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 Salesforce Marketing Cloud (SFMC)
Copy the fixed VML or table wrapper code block from the remediation box above.
Create an 'HTML content' layout block in Content Builder. Paste the table structure. Enclose any custom merge tags inside standard AMPscript wrapper lines.