Firefox is the browser people get stuck on, because it does not use your computer's proxy setting. You can configure Windows or macOS perfectly, watch every other browser start using the proxy, and Firefox will carry on exactly as before.
That is not a bug. Firefox has its own network settings and always has.
Where the setting lives
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Click the menu button (three lines, top right) and choose Settings.
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Stay on the General panel and scroll to the very bottom. It is a long page.
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The last section is Network Settings. Click the Settings… button inside it.
A shortcut: type about:preferences in the address bar, press Enter, then scroll to the bottom.
Setting the proxy
In the window that opens, choose Manual proxy configuration.
For a normal HTTP proxy, which covers most of them:
- Put the address in HTTP Proxy, on its own, like
203.0.113.10. Nohttp://. - Put the number in Port, like
8080. - Tick Also use this proxy for HTTPS.
- Click OK.
That tickbox matters more than it looks. Leave it off and Firefox proxies plain http only, which is a vanishing fraction of the modern web. The proxy appears to do nothing while working exactly as instructed.
For a SOCKS proxy, usually on port 1080:
- Leave the HTTP fields empty.
- Put the address and port in the SOCKS Host row.
- Choose SOCKS v5 unless your provider specifically said SOCKS4.
- Tick Proxy DNS when using SOCKS v5 (see below).
- Click OK.
The DNS setting nobody mentions
Proxy DNS when using SOCKS v5 decides which machine turns a domain name into an IP address.
Leave it unticked and your own computer does the lookups. Your traffic goes through the proxy, but every site you visit is still handed to your internet provider's DNS server in plain sight. You get the proxy's IP address without the privacy that usually motivates using one.
Tick it and the proxy performs the lookups instead.
If privacy is any part of why you are doing this, tick it. It is off by default and it is the single most common reason a SOCKS5 setup leaks the very thing it was meant to hide.
If your proxy needs a username and password
Firefox has nowhere to type them in advance. It waits until you load a page, then shows a login box. Enter them there and tick the option to remember.
Free proxies from public lists have no credentials. If one is asking, it is not yours to use.
Check that it worked
Load any page that reports your IP. You should see the proxy's address.
Testing the proxy before you configure it saves real time here, because Firefox's error messages are vague. Our proxy checker opens an actual connection and tells you whether the address answered, whether it spoke HTTP or SOCKS, and how long it took. That tells you which row to fill in rather than trying both.
Reading the error messages
Firefox is unusually specific if you know what the wording means:
"The proxy server is refusing connections." Firefox reached the address and was turned away. The proxy is down, the port is wrong, or it wants credentials.
The page hangs with no error. Nothing came back at all. Usually a proxy that has gone offline without closing the door behind it.
Only some sites fail. Check the No proxy for box. Anything listed there bypasses the proxy entirely.
Routing only some sites
The built-in settings are all or nothing. No proxy for is the only exception list and it works backwards, naming sites that skip the proxy.
For real per-site control you want an extension. FoxyProxy and SwitchyOmega both hold several proxies at once and pick between them using URL patterns, and both are free. We have separate walkthroughs for each.
Turning it off
Same path, then select Use system proxy settings or No proxy, and click OK.
Because Firefox is independent of the system setting, it makes a useful escape hatch: if a system-wide proxy dies and every other browser stops working, Firefox set to No proxy still loads pages, which is a fast way to confirm that the proxy is the problem rather than your connection.
About free proxies
Most free proxies are machines somebody misconfigured rather than services anybody maintains, and they go offline without notice.
Our free proxy list tests every address continuously by opening a real connection to it, so the uptime figure beside each one is measured rather than promised. That shows you which are alive right now. It cannot make any of them reliable, and nothing else can either.