Overview
Thunderbird is an open-source email client with Gecko engine (like Firefox). CSS support is good but has some quirks.
Documented Quirks
1
Thunderbird Images Context Menu Issue
All versions
Issue
Thunderbird blocks external images by default. Even if users enable them, the context menu may interact oddly.
Workaround
Always provide alt text. Consider asking users to enable images via AMP or notification.
Code Example
<!-- Always include alt text --> <img src="image.jpg" alt="Important content" style="display: block; width: 100%;">
2
Thunderbird and CSS Variables Not Supported
All versions
Issue
Thunderbird doesn't support CSS custom properties (variables).
Workaround
Don't use CSS variables. Use inline styles or plain CSS instead.
Related Resources
- All Email Client Quirks — Browse quirks for other email clients
- CSS Support Matrix — See detailed CSS property compatibility
- Email Client Support Matrix — Compare feature support across clients
- Thunderbird CSS Support — Full CSS property breakdown for Thunderbird