Rather than using browsers based on Firefox (for security reasons), I want to modify Firefox. Which Firefox about:config setting would you recommend changing for speed and privacy?
Thank you.
If your goal is “modify Firefox instead of switching browsers,” the safest approach is to focus on (1) privacy hardening that does not weaken security and (2) avoiding “speed tweaks” that often do little or can backfire. Most meaningful performance gains come from extensions, content blocking, and keeping Firefox lean—not from changing obscure networking limits.
Best single about:config privacy setting (high impact, with trade-offs)
privacy.resistFingerprinting = true
This is Firefox’s main built-in anti-fingerprinting switch. It meaningfully improves privacy against tracking via browser fingerprinting, but it can also cause website quirks (time zone/locale behavior, some canvas/WebGL behaviors, some site compatibility issues). It’s a solid “one setting” recommendation if privacy is the priority and you can tolerate occasional breakage.
Privacy settings I’d change before “speed tweaks” (generally safe)
- Disable telemetry (privacy, not speed)
toolkit.telemetry.enabled = falsedatareporting.policy.dataSubmissionEnabled = falsedatareporting.healthreport.uploadEnabled = false
- Reduce connection “leaks” (minor privacy gain, may slightly reduce convenience/performance)
network.prefetch-next = falsenetwork.dns.disablePrefetch = truenetwork.http.speculative-parallel-limit = 0
- WebRTC (prevents direct IP exposure in some scenarios, but breaks WebRTC calling)
media.peerconnection.enabled = false
Only do this if you do not use browser-based voice/video (Meet, Teams in browser, Discord in browser, etc.).
DNS-over-HTTPS (privacy depends on provider; not automatically “more secure”)
If you want to use DoH, the key pref is:
However, whether this is a privacy improvement depends heavily on which resolver you use and your threat model. If you change this, also review Firefox’s DoH UI settings so you know which provider is used. I would not recommend random DoH changes purely as a “security” tweak without understanding the trade-off (you’re moving DNS visibility from your ISP/network to a DoH provider).
About speed: what I’d recommend (and what I would not)
Meaningful, low-risk “speed” wins from about:config are uncommon today. Many popular “speed tweak” lists change connection limits/caches in ways that can reduce stability, increase memory use, or even slow real browsing.
What actually tends to help performance without risky tweaking:
- Use a reputable content blocker (commonly, uBlock Origin) to reduce script/ad load (often the biggest speed win).
- Keep extensions minimal (each extension can add overhead).
- Leave Firefox’s networking and cache defaults alone unless you have a specific problem you’re solving.
Conclusion
If you change only one about:config key for privacy, use
privacy.resistFingerprinting = true and accept potential site quirks. For “speed,” avoid about:config tweak lists; focus on content blocking and a clean extension set instead.
Sources
www.ctrl.blog
