Firefox — Notes (43.0.4) — Mozilla
https://www.mozilla.org/en-US/firefox/43.0.4/releasenotes/

Fixed:
* Fix for startup crash for users of a third party antivirus tool (Bug 1235537)
* Multi-user GNU/Linux download folders can be created (Bug 1233434)

Changed:
* Re-enable SHA-1 certificates (Bug 1236975)

SHA-1-based certificates with validity period from 2016 will not be validated (Reverted) | Firefox Site Compatibility
https://www.fxsitecompat.com/en-US/docs/2015/sha-1-based-certificates-with-validity-period-from-2016-will-not-be-validated/

2016年から SHA-1ベースの証明書は検証されませんってやってたのを撤回
早すぎたということか