outdated criticisms of Firefox's sandboxing and security has become popular, mostly through competitor browser affiliated people
GrapheneOS, the hardening-focused Android OS, advises users against installing Firefox. Their official usage guide makes several specific security claims about GeckoView [1]:
1. "Firefox has weak internal sandboxing"
2. Gecko-based browsers are "much more vulnerable to exploitation"
3. Firefox "bypass or cripple a fair bit of the upstream and GrapheneOS hardening work"
4. Extension-based privacy protections are "privacy theater"
I researched these claims and published a comparative analysis that maps each one against current evidence. Some are substantiated. Others appear outdated as of 2026.
What I found that may interest Mozilla engineers:
- Firefox has Rust migration that is highest in all mainsteam browsers (Stylo, RLBox, Necko, WebRender) that Chromium does not yet match. Roughly 70% of critical browser CVEs are memory-safety bugs, and Rust eliminates those classes entirely as well.
- Mozilla's own 2025 collaboration with Anthropic's red team [3] and analysis of AI-discovered vulnerabilities suggest ongoing hardening work.
- The dual-engine attack surface argument (Firefox requires Chromium WebView on Android) is a platform architectural constraint, not a Firefox deficiency.
Questions I could not answer from public documentation:
1. Fission shipped on Android in Firefox 147, but the release notes say "the same Site Isolation safeguards already in use by desktop Firefox." Community members noted that unprivileged user namespaces are not available to Android apps. What kernel-level mechanisms does Fission actually use on Android, and how does it differ from desktop?
2. GrapheneOS correctly notes that GeckoView does not use `android:isolatedProcess`. Are there plans to adopt it, or is Mozilla pursuing a different kernel sandboxing strategy?
3. Does Mozilla have internal metrics on what proportion of severity-critical vulnerabilities are found in Rust components versus C++ code paths?
4. Has the desktop Linux sandbox gap with Chromium narrowed since Fission's 2021 desktop release?
https://grapheneos.org/usage#web-browsing
