Sorry, Typo: It's Firefox 39.0a2 :)

I'm fairly sure this isn't supported, actually. Are your sure your certificate isn't falling back to a different algorithm?

This bug is where support for RSA PPS was happening, but it has been around since 2002, and hasn't been updated in over a year.

If you are absolutely sure that it is supported (although I'm fairly sure it isn't), then there is a very large chance it will make it into release. However, nothing is guaranteed. If a change causes major problems, it will be removed. As far as release dates, that won't change. Sometimes, the release will be held back by a few days (rarely up to a week) if there is a major problem with it, but that doesn't happen very often.

Thanks for your answer. Well, at least I can tell it works in FF 39.0a2 and also in FF 40.0a1 whih actually would not be a total surprise as IE and Chrome both support RSA PPS. As always in life: It would be better to actually know than to believe (no offense!): How can the devs be contacted? Somebody needs to know for sure.

See also:

• bug 1088140 - SEC_ERROR_BAD_DER on certificates with RSA-PSS signatures and/or RSA-PSS public keys

Thank you all! One final thing: FF37/38 both have a problem with TLS_RSA_WITH_AES_128_CBC_SHA and TLS 1.2: I habe to turn it off serverwise and only allow for TLS 1.0: Known?