Building Pale Moon seems to fail sometimes/always, depending on to me unknown factors. It builds fine in my NixOS VM, but my NixOS desktop consistently fails with

39:32.01 Executing: /nix/store/p3yihyyg612p3ablgakm1h591spparpp-gcc-wrapper-4.9.4/bin/g++ -std=gnu++11 -Wall -Wc++11-compat -Wempty-body -Wignored-qualifiers -Woverloaded-virtual -Wpointer-arith -Wsign-compare -Wtype-limits -Wunreachable-code -Wwrite-strings -Wno-invalid-offsetof -Wno-error=maybe-uninitialized -Wno-error=deprecated-declarations -Wno-error=array-bounds -fno-exceptions -fno-strict-aliasing -fno-rtti -fno-exceptions -fno-math-errno -msse2 -mfpmath=sse -pthread -pipe -g -O2 -fomit-frame-pointer -fPIC -shared -Wl,-z,defs -Wl,-h,libxul.so -o libxul.so /build/source/pmbuild/toolkit/library/tmp1BqO96.list -lpthread -Wl,-z,noexecstack -Wl,-z,text -Wl,--build-id -B ../../build/unix/gold -Wl,-version-script,symverscript -Wl,-rpath-link,/build/source/pmbuild/dist/bin -Wl,-rpath-link,/nix/store/z8sb116bj3qd3xrb941lv62ifkkmbwzz-palemoon-28.7.1/lib ../../security/nss/lib/crmf/libcrmf.a ../../js/src/libjs_static.a ../../security/nss/lib/nss/libnss3.so ../../security/nss/lib/smime/libsmime3.so ../../security/nss/lib/ssl/libssl3.so ../../security/nss/lib/util/libnssutil3.so ../../config/external/sqlite/libmozsqlite3.so ../../config/external/nspr/pr/libnspr4.so ../../config/external/nspr/libc/libplc4.so ../../config/external/nspr/ds/libplds4.so ../../config/external/lgpllibs/liblgpllibs.so -ldl -lm -ldl -L/nix/store/v0dy9gcr12vf63lyq69nrpgzm3yz5wlz-freetype-2.10.1/lib -lfreetype -L/nix/store/yk3aqhhw3jj0sj9nzqs7vhjx9cwjlb78-fontconfig-2.12.6-lib/lib -lfontconfig -lrt -L/nix/store/690qkhaj8mvr6ax949gz16a69wn5fcxs-libX11-1.6.8/lib -lXrender -L/nix/store/8i03vc4n2a6lhd7s713ahhnhhay04j4a-alsa-lib-1.1.9/lib -lasound -L/nix/store/aldz750xb5k96mzxg4l29dsip28b376k-glib-2.60.7/lib -L/nix/store/jdh4pgqy2w5g9nmzkbljsvks7ljhpz1l-dbus-1.12.16-lib/lib -L/nix/store/lfjjvhm1crj20px5z5pzbhsfxs62nmhw-dbus-glib-0.110/lib -ldbus-glib-1 -ldbus-1 -lgobject-2.0 -lglib-2.0 -L/nix/store/jfwhd03syvpaclfphj41zyaf0lrhp2hz-cairo-1.16.0/lib -L/nix/store/0x8gc2yfpjbrz2w654npqlimh1lw2zqd-gtk+-2.24.32/lib -L/nix/store/cbcbgz17zdhbsbj8fvmqv6hf6y8p13sx-pango-1.43.0/lib -L/nix/store/fgjjmczbhr6m043p14yikshxah0iwnd9-gdk-pixbuf-2.38.1/lib -L/nix/store/djsipbpa5v8pnspcjdwfqw805y3r8qkf-atk-2.32.0/lib -lgtk-x11-2.0 -latk-1.0 -lgio-2.0 -lpangoft2-1.0 -lgdk-x11-2.0 -lpangocairo-1.0 -lpango-1.0 -lcairo -lgdk_pixbuf-2.0 -lX11-xcb -lxcb-shm -lxcb -lX11 -lXext -lXt -lgthread-2.0
39:32.01 /build/source/pmbuild/toolkit/library/tmp1BqO96.list:
39:32.01 INPUT("StaticXULComponentsStart.o")
(alot of INPUTs here)
39:32.12 INPUT("StaticXULComponentsEnd/StaticXULComponentsEnd.o")
39:32.12
39:32.12 collect2: error: ld returned 1 exit status
39:32.13 make[5]: *** [/build/source/config/rules.mk:773: libxul.so] Error 1
39:32.13 make[4]: *** [/build/source/config/recurse.mk:71: toolkit/library/target] Error 2
39:32.13 make[3]: *** [/build/source/config/recurse.mk:33: compile] Error 2
39:32.13 make[2]: *** [/build/source/config/rules.mk:494: default] Error 2
39:32.13 make[1]: *** [/build/source/client.mk:414: realbuild] Error 2
39:32.13 make: *** [client.mk:170: build] Error 2
39:32.17 297 compiler warnings present.
39:32.22 Notification center failed: Install the python dbus module to get a notification when the build finishes.
builder for '/nix/store/p89jk78kyfw30rh12ibsk1gkrjf0jbjv-palemoon-28.7.1.drv' failed with exit code 2
error: build of '/nix/store/p89jk78kyfw30rh12ibsk1gkrjf0jbjv-palemoon-28.7.1.drv' failed

it's possible this also caused this build here to fail?

This also happened to me before this update, so it's not a blocker for it, but it's definitely not good either...

Looking at

Notification center failed: Install the python dbus module to get a notification when the build finishes.

it checks for the existence of a dbus session bus to provide a notification.
On a build on hydra this won't happen, so likely the reason why it doesn't try to bring in that additional buildtime dependency.
My advice would be to completely remove that code with a patch. It's not friendly for a nix build.

it checks for the existence of a dbus session bus to provide a notification.
On a build on hydra this won't happen, so likely the reason why it doesn't try to bring in that additional buildtime dependency.

You mean the dbus dependencies? I'll check if that's the only thing they're required for and remove them if that's the case.
It actually seems to be tripping before the actual contact with dbus, while trying to import a Python dbus library, but ofc there's no point in having any of that enabled on Hydra.

                try:
                    import dbus
                except ImportError:
                    raise Exception('Install the python dbus module to '
                        'get a notification when the build finishes.')

My advice would be to completely remove that code with a patch. It's not friendly for a nix build.

I know bugger-all about Python or the mach build system, so I don't feel comfortable meddling with that and patching out stuff, but I think i found a flag to disable just the notification stuff. I'll submit it once I've tested locally that it works properly.

The notifications within the program or at build time?

If you aren't able to work it out I could write a patch for you.

The "Notification center" is for build-time notifications. (I think)
There's an environment variable it checks before attempting to print anything, looking for other references to that environment variable within the code base on GitHub gives no further results:

        moz_nospam = os.environ.get('MOZ_NOSPAM')
        if moz_nospam:
            return

I'm running a test build right now with that variable set. If it works, it should be enough right?

Yep, appears to just return if that variable is in the environment.

Added the MOZ_NOSPAM variable and pinned the used GCC version to 7.* according to this recommendation I found.
Can't do much testing of the binary rn and haven't figured out why I can't build it locally on my desktop, but it compiles fine in my VM and appears to be working at first glance.

@GrahamcOfBorg eval

Obsoleted by #72598
Non-update changes superseded by #76728