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Firefox maker Mozilla disabled support for the protocols TLS 1.0 and TLS 1.1 in recent versions of the Firefox Nightly web browser.

Major browser makers such as Mozilla and Google announced in 2018 that support for the decade-old standards would be dropped in 2020 to improve the security and performance of Internet connections. Back then it was revealed that TLS 1.1 was used by 0.1% of all Internet connections; the number has likely gone done in the meantime.

Transport Layer Security (TLS) is a security protocol used to encrypt Internet traffic; TLS 1.3 Final was published in 2018 and companies started to integrate the final version into browsers shortly thereafter.

Mozilla started to enable TLS 1.3 in Firefox Stable in 2018, and other browser makers such as Google added support for the new protocol version as well.

Tip: here is a way to determine if your browser supports TLS 1.3 and other security features.

Firefox and TLS 1.0 and 1.1 deprecation

Mozilla disabled support for TLS 1.0 and TLS 1.1 in Firefox Nightly in preparation for the deprecation in Firefox Stable in 2020. A quick check on a SSL Labs test site confirms that TLS 1.2 and 1.3 are the only supported protocols by the browser.

Sites that support TLS 1.0 and/or TLS 1.1 but not TLS 1.2 or newer will fail to load and throw a "secure connection failed" error instead. The error code is SSL_ERROR_UNSUPPORTED_VERSION.
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