Mozilla has released a minor update to the current Firefox 43 branch with Firefox 43.0.1 on December 18th. This is part 1 of 2 for the fix of Bug 1079858. This bug has to do with Microsoft deprecating the use of the SHA1 Authenicode signatures for Windows singing on January 1st, 2016. Mozilla is moving to use SHA2 signature algorithms and the purpose of this patch is to simply inform the updater and maintenance service of the new SHA2 certificate issuer. Part 2 which will be released with Firefox 43.0.2 likely in the next week will Use SHA-2 to sign Windows binaries, and switch the stub installer to expect that.
Warning: Windows XP SP2 or older users will no longer be able to get Firefox updates or run anything newer than Firefox 43 as Windows XP SP2 does NOT support SHA2 (or newer) signature algorithms. Windows XP SP3 and newer users will still be able to run newer versions of Firefox.
Important: User who do not update to Firefox 43.0.1 and the future 43.0.2 may encounter difficulties (UAC Prompts or Windows blocking the updater service) installing upcoming version of Firefox