Change:
firefox-unwrapped = common { pname = "firefox"; <del> version = "51.0.1"; sha512 = "556e31b717c0640ef5e181e00b9d2a6ea0ace7c16ae04333d0f2e9e120d0ab9efe82a4ca314ef43594c080523edf37953e65dbf694c7428be0a024f3719d8312"; </del> <ins> version = "52.0"; sha512 = "bffe5fd9eee240f252bf8a882c46f04551d21f6f58b8da68779cd106ed012ea77ee16bc287c847f8a7b959203c79f1b1d3f50151111f9610e1ca7a57c7b811f7"; </ins> updateScript = import ./update.nix { attrPath = "firefox-unwrapped"; inherit writeScript lib common-updater-scripts xidel coreutils gnused gnugrep curl;

Discussion:
checking for nss-config. /nix/store/mjbccpz6whnaj54z8dmzv055r0w97y8b-nss-3.28.1-dev/bin/nss-config checking for NSS - version = 3.28.3. no configure: error: you don't have NSS installed or your version is too old DEBUG: <truncated - see for full outputDEBUG: #include <malloc.hDEBUG: #include <stddef.hDEBUG: sizet mallocusablesize(const void ptr); DEBUG: int main() { DEBUG: return mallocusablesize(0); DEBUG: ; return 0; } DEBUG: configure:9923: checking for valloc in malloc.h DEBUG: configure:9948: checking for valloc in unistd.h DEBUG: configure:: checking NSPR selection DEBUG: configure:: checking for nspr-config DEBUG: configure:: checking for NSPR - version = 4.13.1 DEBUG: configure:: /nix/store/wgvrkijby0awhqkyfkj0qp9cc4921hd9-gcc-wrapper-5.4.0/bin/gcc -std=gnu99 -c -fno-lifetime-dse -fno-strict-aliasing -ffunction-sections -fdata-sections -fno-math-errno -pthread -I/nix/store/z1bz064xx99pggzvzx44v3pcn7sxz4x4-nspr-4.13.1-dev/include conftest.c 1&5 DEBUG: configure:: /nix/store/wgvrkijby0awhqkyfkj0qp9cc4921hd9-gcc-wrapper-5.4.0/bin/gcc -std=gnu99 -c -fno-lifetime-dse -fno-strict-aliasing -ffunction-sections -fdata-sections -fno-math-errno -pthread -I/nix/store/z1bz064xx99pggzvzx44v3pcn7sxz4x4-nspr-4.13.1-dev/include conftest.c 1&5 DEBUG: configure:: /nix/store/wgvrkijby0awhqkyfkj0qp9cc4921hd9-gcc-wrapper-5.4.

0/bin/gcc -std=gnu99 -c -fno-lifetime-dse -fno-strict-aliasing -ffunction-sections -fdata-sections -fno-math-errno -pthread -I/nix/store/z1bz064xx99pggzvzx44v3pcn7sxz4x4-nspr-4.13.1-dev/include conftest.c 1&5 DEBUG: configure:: checking for libevent DEBUG: configure:: checking MOZLIBEVENTCFLAGS DEBUG: configure:: checking MOZLIBEVENTLIBS DEBUG: configure:: checking for nss-config DEBUG: configure:: checking for NSS - version = 3.28.3 DEBUG: configure: error: you don't have NSS installed or your version is too old ERROR: old-configure failed builder for ‘/nix/store/yag51knblmw3zlydgrxy1rhg4qp8lh5h-firefox-esr-unwrapped-’ failed with exit code 1 cannot build derivation ‘/nix/store/dyfp6l09n7215p684xvxv7pjs90qf89c-firefox-’: 1 dependencies couldn't be built cannot build derivation ‘/nix/store/444f6d621mg1fprgkg0chw4dxcjsd71y-system-’: 1 dependencies couldn't be built cannot build derivation ‘/nix/store/c6d6aprdj1bqbmvkffc8fqk8qfsc70v6-nixos-system-toadman-’: 1 dependencies couldn't be built error: build of ‘/nix/store/c6d6aprdj1bqbmvkffc8fqk8qfsc70v6-nixos-system-toadman-’ failed add firefox to package list in your nix then nixos-rebuild switch 09pre102933. (Hummingbird) nix-env (Nix) 1.11.7 "17.09pre102933." System: (NixOS: , Ubuntu/Fedora: , ...) Nix version: (run ) Nixpkgs version: (run )
I've been seeing those build failures too. Investigating recent firefox updates ...
See
The firefox tests now reliably , on both x86 platforms, so the channel would not update.

I haven't heard of real-life problems with the updated firefox, though.
If tests block the channel, how could FF 52 get into the channel when it wouldn't even build? Were the segfaults related to ? Anyway, seems fixed now. Latest channel update has nss 3.28.3 and updated icu and sqlite, and FF is available from hydra.
I'm not sure how this happened. Maybe it was some misunderstanding. I certainly agree to close.