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Fix Outlook Button Border Collapsing in Mozilla Thunderbird — Klaviyo Guide

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

Root Bug Analysis

Mozilla Thunderbird uses the Gecko which lacks support for standard rendering rules. This causes Outlook Button Border Collapsing elements to break or collapse when rendering templates.

Active rendering engine: Gecko

Klaviyo Specific Guide

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

Integration Step:

Open your Klaviyo template editor. Drag an 'HTML' block directly into your layout timeline (do not use a standard text box). Clear the default skeleton content inside the Klaviyo markup editor and paste the RenderOps corrected inline code.

ESP Unsubscribe Alignment

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

Klaviyo Unsubscribe Tag:{% unsubscribe %}

Documented Client Behavior

Expected layout behavior based on target rendering engine specifications:

Documented behavior: Outlook Button Border Collapsing causes elements to stack vertically or clip in Mozilla Thunderbird when templates are sent from Klaviyo.

Interactive Klaviyo Custom Sandbox

Target Environment: Mozilla Thunderbird

Auto-compile fixes inside RenderOps Workspace

Load layout code directly into our VML Button Builder to compile responsive table frameworks that display cleanly in Mozilla Thunderbird.

Launch VML Button Builder

Fix Outlook Button Border Collapsing on Other clients for Klaviyo