Fix CSS Flexbox Collapse in Mozilla Thunderbird — Campaign Monitor Guide for Financial Services & Banking
Financial emails carry high-compliance requirements. Layout collapses, overlapping text, or accessibility failures can lead to compliance audits and client confusion. Below is the targeted integration guide to fix CSS Flexbox Collapse inside Mozilla Thunderbird templates when using Campaign Monitor.
Technical Breakdown
Mozilla Thunderbird uses the Gecko which lacks support for standard rendering rules. This causes CSS Flexbox Collapse 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. Enforce strict WCAG color contrast standards across your statement tables and summary grids to ensure legibility and regulatory compliance.
Remediation Code Block
To resolve this, modern layouts must be compiled down to Outlook-compliant nested HTML table models. Each flex container becomes a table row, and each flex child becomes a table data cell (td) with explicit pixel or percentage widths. In your Campaign Monitor campaign manager, make sure you configure your links to run via [unsubscribe].
<table role="presentation" border="0" cellpadding="0" cellspacing="0" width="100%">
<tr>
<td width="50%" valign="top" style="padding: 20px;">Column 1</td>
<td width="50%" valign="top" style="padding: 20px;">Column 2</td>
</tr>
</table>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.