6.6.9 — Security and stability improvements

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 browsing data is collected but Waterfox may contact Mozilla’s certificate update endpoints to fetch missing intermediate certificates and revocation data.

Stability

• Printer driver isolation (Windows): Printer drivers are now loaded in a separate process, preventing buggy drivers from crashing Waterfox. This uses Windows’ application-level printer driver isolation to keep third-party driver issues from bringing down the browser.

Performance

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

Experimental

• Ogg Theora support can be re-enabled by setting media.theora.enabled to true in about:config.

Contributors

Thanks to @goodusername123 for their contributions to the JPEG-XL improvements, printer driver isolation and Ogg Theora backport in this release.