Quick Answer

Firefox HTTPS-Only Mode tries to open sites with encryption and warns if a secure connection is unavailable. Enable it in desktop Firefox's connection security settings. If an old device only offers HTTP, confirm the address through a trusted source and keep any exception limited to that device. Avoid sending sensitive information over HTTP.

Turn it on and recognise the warning

Open Firefox Settings and look for HTTPS-Only Mode under privacy or connection security. Set the mode for the scope you intend to protect. If you land on a warning, check the address for a typing error. Use a trusted bookmark or the service's official address when you can. If the service offers an encrypted route, choose that instead of continuing over HTTP.

The warning does not necessarily mean your internet is down. It can mean Firefox tried a secure address and could not use it. Open a known working HTTPS site in a second tab. If the second site works, test the original address separately before changing any setting that applies to every website. If every site fails, investigate connectivity independently.

Respond to a connection warning

Treat old device pages as exceptions

An older device on your own network may publish a setup page over HTTP. Confirm its address from the device documentation or an administrator before continuing. If you decide to add a site exception, keep the scope as narrow as the browser offers and remove it when no longer needed. Do not use this as a way around certificate errors on other services or as a reason to put personal information into a web page whose identity you cannot verify.

A page being reachable from your home or office does not make it encrypted. If it accepts credentials, prefer a secure setup method when one is available. When you cannot confirm whether the device supports one, get its exact model and software version and ask the person who manages it. Avoid guessing from the login screen.

Separate the related browser settings

HTTPS-First and HTTPS-Only are different Firefox behaviours. One tries a secure route first under certain conditions, while the stricter mode can stop at a warning before opening an unencrypted page. DNS over HTTPS is a different setting again: it concerns name lookups, not encryption of all traffic to a website. Check the name of the setting you are changing before testing the result.

The browser setting costs R0 and does not need new computer hardware. If you have an unrelated replacement planned, you can compare mini pcs and all laptops on special by their intended use; that will not add HTTPS support to a separate old device. After troubleshooting, revisit the original address once with the intended protection in place so you know which route the page uses.

Frequently Asked Questions

Does HTTPS-Only Mode encrypt an HTTP-only server?

No. It tries a secure connection and warns when that route is unavailable.

Where is the setting in desktop Firefox?

Look in Settings under privacy or connection security for HTTPS-Only Mode.

Should I turn it off for all sites?

If you need an exception, keep it limited to the verified site and review it afterwards.

Is a router page automatically safe because it is local?

No. Verify the address and prefer a secure management method if available.

Is HTTPS-Only the same as DNS over HTTPS?

No. One concerns website connections; the other concerns domain name lookups.

Does a single warning mean my connection is down?

No. Test a known HTTPS site separately to see whether the failure is limited to one address.

Keep the exception narrow Confirm the device address and leave encryption enabled elsewhere.