Currently, as per the CSS @font-face specification, Firefox does not support platform substitution for fonts specified using local() in the src property. The spec states that "Platform substitutions for a given font name must not be used," which is generally in line with font rendering consistency across platforms. However, in some use cases, especially when controlling font rendering via fontconfig (on Linux platforms), it's necessary to allow platform-specific font substitutions for more precise control over which fonts are used. This is especially important in environments where custom fonts are preferred or where system fonts must be substituted due to specific user preferences or system configurations. Feature Request: It would be incredibly useful if Firefox could provide an option (likely in the settings or via about:config) to enable platform-based font substitution when using the local() function in @font-face. This would allow users to take advantage of fontconfig (or similar platform-specific font management systems) to replace the font with an appropriate system font based on configuration, without requiring changes to the web font itself.
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