How Can I Fix Firefox's Cross-Domain Font Loading Issues with Amazon S3 CORS?

Amazon S3 CORS and Firefox Cross-Domain Font Loading: Resolving Font Loading Issues

Firefox has been known to encounter issues loading fonts from a different origin than the current webpage, particularly when fonts are hosted on CDNs. This problem has been widely discussed in online forums, including the one cited.

To address this challenge, Amazon S3 CORS (Cross-Origin Resource Sharing) offers a potential solution. CORS allows servers to specify resources that can be accessed from other domains, thereby mitigating cross-domain security restrictions.

To configure CORS for S3, an XML document must be uploaded to the bucket containing the fonts. The following configuration is recommended:

<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
    <CORSRule>
        <AllowedOrigin>https://mydomain.com</AllowedOrigin>
        <AllowedMethod>GET</AllowedMethod>
        <MaxAgeSeconds>3000</MaxAgeSeconds>
        <AllowedHeader>Content-*</AllowedHeader>
        <AllowedHeader>Host</AllowedHeader>
    </CORSRule>
    <CORSRule>
        <AllowedOrigin>https://*.mydomain.com</AllowedOrigin>
        <AllowedMethod>GET</AllowedMethod>
        <MaxAgeSeconds>3000</MaxAgeSeconds>
        <AllowedHeader>Content-*</AllowedHeader>
        <AllowedHeader>Host</AllowedHeader>
    </CORSRule>
</CORSConfiguration>

This configuration allows:

• GET requests from the specified origin (mydomain.com)
• Subdomains of the specified origin
• Sets the maximum age of CORS headers to 3000 seconds
• Allows request headers that begin with "Content-" and "Host"

However, due to Cloudfront's caching of the Access-Control-Allow-Origin header, some developers have reported issues with cross-domain font loading. To overcome this, a workaround is to use a query string to differentiate between calls from different domains:

curl -i -H "Origin: https://a.domain.com" http://hashhashhash.cloudfront.net/font.woff?https_a.domain.com

This approach allows Cloudfront to serve unique responses for different domains, bypassing the caching issue.

In conclusion, using Amazon S3 CORS along with the query string workaround can resolve Firefox's cross-domain font loading issues. If further assistance is required, refer to the cited AWS forum thread for additional insights and explanations from Amazon experts.

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