Firefox on Windows not using your proxy (or leaking your real IP)? Privacy-safe fixes

When a proxy is misconfigured, it can feel like everything is “on,” but some traffic quietly goes around it. On Windows, Firefox can also behave differently depending on whether it’s using system settings, its own proxy settings, or DNS-over-HTTPS.

Let’s fix it in a way that keeps your troubleshooting as privacy-safe as possible.

Before you start: If you’re doing this on a work/school network, proxy changes may be managed by policy. Don’t try to bypass restrictions—focus on getting the intended configuration working.

1. Confirm what kind of proxy you actually have (HTTP(S) vs SOCKS)

Privacy-safe troubleshooting starts with accuracy: many “proxy not working” cases are simply the wrong proxy type entered.

• HTTP/HTTPS proxy: Usually provided as host + port, sometimes with username/password. Often only proxies browser traffic.
• SOCKS5 proxy: Common for privacy tools; can proxy more traffic types. In Firefox, SOCKS has extra options that matter.

If your provider gave you a single “endpoint,” verify whether it’s HTTP(S) or SOCKS5. Mixing them can make Firefox fail over to a direct connection without being obvious.

2. Set Firefox to use a manual proxy (don’t rely on “Use system proxy settings” yet)

Using Windows system proxy settings can be fine, but it adds another moving piece. For privacy-safe troubleshooting, temporarily configure Firefox directly so you’re testing one layer at a time.

• In Firefox, open Settings → search for Network Settings → click Settings…
• Select Manual proxy configuration
• Enter the proxy Host and Port exactly as provided
• If you have an HTTP proxy and want it to apply broadly, consider checking Use this proxy server for all protocols (only if your provider supports it)

Keep this change temporary. Once things work, you can decide whether to keep Firefox-only settings or move back to Windows system proxy settings.

3. If you use SOCKS, enable remote DNS to avoid DNS leaks

One of the most common privacy surprises: your web traffic goes through the proxy, but DNS lookups still go to your normal DNS resolver (often your ISP). That can reveal what sites you’re visiting, even if the page loads via proxy.

• In the same Network Settings dialog, if you’re using SOCKS v5, check Proxy DNS when using SOCKS v5 (wording may vary slightly)

If your proxy is HTTP(S) (not SOCKS), that checkbox won’t help—DNS handling depends on other settings (next step).

4. Align DNS-over-HTTPS (DoH) with your proxy goal (don’t “double route” by accident)

Firefox can resolve DNS in multiple ways. If you’re aiming for privacy, you want DNS behavior to be intentional—either through the proxy (ideal with SOCKS + remote DNS), or through DoH, or through your system DNS, but not a confusing mix.

• Firefox Settings → search DNS → Enable DNS over HTTPS
• If you’re using SOCKS5 + Proxy DNS, you may prefer turning DoH off so DNS stays with the proxy route.
• If you’re using an HTTP proxy, DoH can be on or off, but be aware it may send DNS directly to the DoH provider, which can bypass your proxy path depending on setup.

For privacy-safe troubleshooting, pick one approach and stick with it while testing. Changing two variables at once makes leaks harder to diagnose.

5. Remove proxy bypass rules that silently force direct connections

Firefox and Windows can both have “no proxy for” lists. These are useful for intranet sites, but they can also create the feeling that the proxy “sometimes works, sometimes doesn’t.”

• In Firefox Network Settings, check the No Proxy for box/list.
• Temporarily remove entries you don’t recognize (or clear the list) while testing.
• Watch for patterns like .local, internal domains, or IP ranges (these may be expected on managed networks).

If the issue is a bypass rule, fixing it is usually just tightening the list to only what you truly need.

6. Test with a fresh Firefox profile (privacy-safe, avoids extensions and cached proxy auth)

Extensions, cached credentials, and old network prefs can override proxy behavior. A new profile is a clean test without uninstalling anything.

• Type about:profiles in the Firefox address bar
• Click Create a New Profile
• Open the new profile and configure the proxy once (minimal changes)

If the proxy works in the new profile, the problem is likely an extension, a custom network preference, or saved proxy authentication in your main profile.

7. Watch for “transparent proxy” or captive portals (don’t enter credentials on the wrong page)

Some networks intercept traffic (hotels, coffee shops, campuses). That can break proxies or make you think the proxy is failing.

• If pages redirect oddly, open a new tab and try a simple non-sensitive site you don’t log into.
• Complete any captive portal step before turning on your proxy, if required.
• Avoid typing proxy credentials into random popups—only enter them in Firefox’s built-in auth prompt for the proxy host you expect.

This is more about staying safe than “fixing,” but it prevents accidental credential leaks.

8. When to switch back to Windows system proxy (and how to keep it tidy)

Once your proxy works reliably in Firefox with manual settings, you can decide whether you want it system-wide.

• If you only need proxying inside Firefox, keep the Firefox manual settings (simpler, less risk of affecting other apps).
• If you need multiple apps to use it, configure Windows proxy settings and then set Firefox to Use system proxy settings.
• After switching, re-check that Firefox didn’t reintroduce a bypass list or different DNS behavior.

Keeping Firefox and Windows aligned reduces “it works in one place but not the other” confusion.

Final thoughts

Privacy-safe proxy troubleshooting is mostly about reducing variables: one proxy method, one DNS strategy, and a clean profile when needed.

If you still see signs of leaks after these steps, treat it as a configuration mismatch (especially DNS) rather than assuming the proxy is “broken.”