As part of Firefox 31’s release, Mozilla made a change to enable support for NT LAN Manager version 1 (NTLMv1) network authentication when connecting to sites that are using HTTPS to allow encrypted communication via SSL between Firefox 31 and the website in question. This is to address the change made in Firefox 30, which disabled support for NT LAN Manager version 1 (NTLMv1) network authentication for sites using either HTTP and HTTPS.
NTLMv1 authentication to sites using HTTP is still disabled by default. For more information on why HTTPS is now enabled while HTTP remains disabled, this Mozilla bug report discusses the issue.
A way to tell if the NTLMv1-using site you’re trying to access is using HTTP or HTTPS is to check the connection address. If it begins with https://, you should be OK. If it begins with http:// , Firefox 31 will still block NTLMv1 authentication.
If you need to enable NTLMv1 authentication for an HTTP site that uses NTLMv1 authentication, Mozilla has provided a workaround to non-Windows users of Firefox, in the form of a setting that can be toggled to allow NTLMv1 authentication. This workaround should allow Mac and Linux users to continue using NTLMv1 authentication on HTTP sites, which will allow access again to SharePoint-based or IIS-backed web applications. For those folks who need it, I have the workaround documented here.
