Aside from a website potentially experiencing server-side SSL issues, it’s possible your Firefox settings are causing a miscommunication between the website server and your computer. This is a far likelier case if many different websites are throwing the error code SSL_ERROR_NO_CYPHER_OVERLAP.
You should always keep Firefox up to date anyhow, but an outdated version of Firefox is a potential cause of Firefox error SSL_ERROR_NO_CYPHER_OVERLAP appearing.
If either TLS or SSL3 are disabled or otherwise misconfigured in your Firefox TLS settings, the error code will also commonly spring up. Finally, any website that uses RC4 (Rivest Cipher 4) in its encryption will run into issues with Firefox TLS no matter what. This is because RC4 was prohibited from TLS in 2015.
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Update Firefox. You should always keep Firefox up to date anyhow, but an outdated version of Firefox is a potential cause of Firefox error SSL_ERROR_NO_CYPHER_OVERLAP appearing.
Force Firefox TLS settings to 1.3. Open a new tab and type about:config into the URL bar. If Firefox directs you to a warning page, select Accept the Risk and Continue. When you land on the Advanced Preferences page, type tls into the search bar underneath the regular Firefox URL bar. In the results, you’re looking for security.tls.version.max, which should be set to 4 under normal circumstances.
If it’s set to something else, select the pencil icon to the far right of security.tls.version.max and change the number to 4.
Loosen Firefox encryption protocol. Another way to stop Firefox error code SSL_ERROR_NO_CYPHER_OVERLAP is by disabling the protection that blocks Firefox from accessing websites that it deems unsafe. To do this, select the Options menu > Privacy & Security, scroll down to Security, then select Block dangerous and deceptive content to disable it.