6.6.9 - Security and stability improvements

Waterfox 6.6.9 includes security updates, a certificate reliability fix, and a minor performance improvement.

Security

• Fixed multiple security vulnerabilities as described in Mozilla Foundation Security Advisory 2026-15.
• Fixed 3 CVEs in the JPEG-XL image decoder.

Bug Fixes

• Certificate reliability improvements: Fixed an issue that could cause “Unknown Issuer” certificate errors on certain sites, most commonly on Linux. Waterfox now refreshes intermediate certificate data as needed to keep HTTPS sites loading securely. No new browsing data is collected; Waterfox may contact Mozilla’s certificate update endpoints to fetch missing intermediate certificates and revocation data.

Performance

• Small performance improvement in JPEG-XL image decoding (improved LUT loading and added RGB offset dithering).