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Fix CSS Grid Broken Columns in Mozilla Thunderbird — ActiveCampaign Guide

A programmatic integration guide for resolving email rendering crashes inside Mozilla Thunderbird using ActiveCampaign's layout editor environment.

Root Bug Analysis

Mozilla Thunderbird uses the Gecko which lacks support for standard rendering rules. This causes CSS Grid Broken Columns elements to break or collapse when rendering templates.

Active rendering engine: Gecko

ActiveCampaign Specific Guide

ActiveCampaign's delivery wrapper can clean and restructure elements during import, creating dynamic spacing differences inside Mozilla Thunderbird.

Integration Step:

Insert an 'HTML block' from the layout builder panels. Avoid standard text boxes, as the ActiveCampaign parser might strip conditional MSO comment strings on saving.

ESP Unsubscribe Alignment

When compiling custom HTML templates for ActiveCampaign, you must ensure your layout retains deliverability compliance loops. ActiveCampaign requires you to insert their specific unsubscribe merge tag, otherwise your campaign delivery will be flagged by automated spam audits.

ActiveCampaign Unsubscribe Tag:%UNSUBSCRIBELINK%

Documented Client Behavior

Expected layout behavior based on target rendering engine specifications:

Documented behavior: CSS Grid Broken Columns causes elements to stack vertically or clip in Mozilla Thunderbird when templates are sent from ActiveCampaign.

Interactive ActiveCampaign Custom Sandbox

Target Environment: Mozilla Thunderbird

Paste Your Broken Code

<div style="display: grid; grid-template-columns: 1fr 1fr; gap: 10px;">
  <div>Col 1</div>
  <div>Col 2</div>
</div>

RenderOps Compiled Output

<!-- Paste code on the left and click compile to output clean fallback tags -->

Auto-compile fixes inside RenderOps Workspace

Load layout code directly into our Flexbox→Table Compiler to compile responsive table frameworks that display cleanly in Mozilla Thunderbird.

Launch Flexbox→Table Compiler