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If websites stop loading while you use a proxy, first check whether the problem affects one site or every site, then compare browsers and proxy settings. A proxy that cannot reach the internet can block browsing, but turning it off is not always the right fix: work and school networks may require administrator-managed proxy settings.
1. Find out how widespread the problem is
- Open a different website in the browser that is failing.
- Try the affected website in another browser.
If only one browser fails, focus on that browser’s proxy configuration, extensions, security-software permissions, or profile. If multiple browsers fail, investigate the network and proxy connection rather than treating it as a Firefox-only issue. Mozilla recommends testing another browser and checking whether the proxy server can connect to the internet: Mozilla’s “Server Not Found” troubleshooting guide.
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2. Compare the browser’s proxy settings
Firefox
In Firefox, open Settings and find Network Settings or its proxy settings. Compare the selected configuration with the system settings or a browser that works. Firefox has its own connection settings, so a mismatch can explain why one browser fails while another does not. Mozilla’s guide to Firefox connection settings explains the available choices.
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If this is a personal connection and you do not use a proxy, selecting No Proxy is a reasonable diagnostic step. If you know you use a proxy, compare its settings rather than guessing at an address or port. On a work or school device, do not remove a required proxy or alter a managed setup without checking with IT.
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Windows proxy configuration
Windows can use automatic detection, an organization-provided setup script, or a manually configured proxy server name or address and port. An administrator may also configure exceptions that send specific sites directly rather than through the proxy. See Microsoft’s Windows proxy settings guidance for the available options.
If only certain sites fail, the cause may be a proxy exception, a setup-script (PAC) routing rule, or an organization’s proxy policy. PAC files can route some destinations directly and others through a proxy. Ask the person who manages the configuration to check the relevant rule instead of changing a managed setting yourself. Mozilla also advises users who lack the proxy details to contact their network administrator.
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3. Use the error message to choose a troubleshooting branch
Browser error text is a clue, not proof that the proxy is at fault. Google’s Chrome connection-error guidance describes these common errors:
| Error | What it can indicate | What to check |
|---|---|---|
ERR_NAME_NOT_RESOLVED |
The hostname could not be resolved, or it may not exist or may point to a different IP address. | Try another site and check whether the failing address is correct. If many sites fail, investigate network and proxy connectivity. |
ERR_CONNECTION_TIMED_OUT |
The connection took too long; connectivity may be slow, or the page may be busy. | Try another site and retry later. If the issue affects many destinations, check the network and proxy. |
ERR_CONNECTION_RESET |
The connection was interrupted. | Check whether the interruption occurs in more than one browser or on more than one site. |
ERR_CONNECTION_REFUSED |
The destination may be rejecting or blocking the connection. | Compare other sites and check whether a proxy rule or destination policy applies. |
ERR_EMPTY_RESPONSE |
The page sent no data and may be down. | Test another site before changing proxy settings. |
If HTTPS sites fail but HTTP sites work
HTTPS commonly travels through an HTTP proxy using the CONNECT method, which creates a tunnel to the destination. Some proxies do not support CONNECT, or restrict it to certain ports. A proxy configuration or policy may therefore allow some traffic while blocking HTTPS destinations. The MDN explanation of HTTP CONNECT describes these limitations.
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If you see a certificate-authority error on a managed network
Some organizations inspect HTTPS traffic through a managed proxy. In that situation, the browser may need the organization’s certificate; Google notes that a missing or uninstalled certificate can cause certificate errors. Contact your administrator rather than installing an unfamiliar certificate yourself. Google warns, “It isn’t recommended that you install a certificate on your own, as it’s usually a security risk.”
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.4. If the problem is limited to one browser
Check extensions, site data, and security software
- Temporarily disable extensions one at a time, then retry the site. In Chrome, an Incognito test can help identify whether an extension is involved.
- If only particular sites fail, clear that site’s cookies and cached data, then try again.
- Check whether antivirus or firewall software began blocking the browser, especially after a browser or security-software update. For certificate errors, Chrome’s guidance also suggests checking antivirus HTTPS scanning. Restore protection after any temporary diagnostic change.
- On Wi-Fi, check whether a captive portal requires you to sign in before internet access is available.
Mozilla’s Firefox troubleshooting guide for cases where other browsers work covers proxy settings, extensions, cookies and cache, and security software.
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Leave advanced Firefox preferences for last
Mozilla also documents DNS-prefetch and IPv6 preferences as advanced troubleshooting. Changing them is not a first-line fix: Mozilla warns that changes in about:config can affect Firefox stability, security, and performance. Try the basic checks above first, and avoid changing advanced preferences unless you understand the setting and have a specific reason to test it.
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Organization-managed proxies may depend on a setup script, server address, port, certificate, exception list, or policy that you cannot safely infer from the browser error. Keep a required proxy enabled, note which sites and browsers fail, and give those details to IT. Do not substitute a public proxy, invent a server address, or install a certificate found elsewhere as a workaround.
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