Since bug 1096494, we're not signing the NSS libraries with shlibsign on mac, which means FIPS mode can't be switched to anymore. The "fun" thing is that the .chk files can't be under Content/MacOS anymore because of OSX app signature, so bug 1100424 is required to make FIPS mode possibly work again. We might not care about FIPS mode, but from the comments in bug 1096494, it doesn't seem there has been a really conscious decision made whether we do or not, so I'm raising this again here.

Another funny detail: with some mac builds happening on linux hosts, signature would also require to figure out how to get a working linux shlibsign to do the signing for the mac build.

I think we should just WONTFIX this. I argued for not worrying about generating these files in the original bug, and I think that still stands. Per bug 1096494 comment 31 it doesn't seem like anyone actually needs FIPS mode in Firefox, at least for government use, and it's not clear who else would actually be using it. (duplicated this comment from bug 1100424)

I agree. Bug 1370667 will make it impossible to enable FIPS on the NSS version we ship with Firefox.