I tested the latest Firefox beta using https://cc.dcsec.uni-hannover.de/ and all ciphers supported by Firefox 25 use MAC SHA1; none of them allow SHA-2. Can this be changed? Do Mozilla have plans to use SHA-2 in the future?
Besides, when I try to access a site which supports only SHA-2 MACs, I get an error.
I tested on Ubuntu 13.10 using
ppa:mozillateam/firefox-next to have Firefox using NSS 3.15.1 and the result was the same: no SHA256 ciphers were available. Chrome (with >= NSS 3.15.1) and Opera work fine.