Firefox version 43.0.2 (12/22/2015) is available via the program's internal updater (Help / About Firefox)
There are no release notes as of the moment...
https://www.mozilla.org/en-US/firefox/43.0.2/releasenotes/
Changed - Use a SHA-256 signing certificate for Windows builds, to meet new signing requirements
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Remark: 43.0.1 was released to PREPARE to use this signing certificate. 43.0.2 apparently implements such use.